January Transfers: Which Signings Actually Made a Difference?

The January transfer window has a reputation as a panic-buy bazaar. Clubs overpay for players they wouldn't look twice at in the summer, desperate managers convince their boards to sanction emergency deals, and the success rate for mid-season signings is historically dire.

But every now and then, a January signing transforms a team's season. With six to eight weeks of data since the window closed, we now have enough sample size to assess which signings from January 2026 have genuinely moved the needle for their new clubs.

Here's our data-driven assessment, ranked by impact.

The Hits

Leandro Trossard's Move to Atletico Madrid

Wait, hear us out. Trossard leaving Arsenal raised eyebrows, but at Atletico Madrid, he's been a revelation. Freed from the rotation roulette at the Emirates, the Belgian has started every game since arriving and his numbers are outstanding.

His xG + xA per 90 minutes at Atletico is 0.71 -- significantly higher than his 0.48 at Arsenal this season. Part of that is system fit: Simeone's direct style gives Trossard more opportunities to run at defenders and create in one-on-one situations, which plays to his strengths.

Atletico's team xG per game has risen from 1.52 before Trossard's arrival to 1.89 since. You can't attribute all of that to one player, but the correlation is striking. He's added a creative dimension that Atletico were sorely lacking, and his work rate out of possession has been exactly what Simeone demands.

Verdict: Genuine impact signing. Both clubs may have gotten what they needed.

Joao Felix to Aston Villa

After years of bouncing around on loans, Joao Felix appears to have found a home at Villa Park. Unai Emery's structured system gives Felix the freedom to roam between the lines, and his creative output since arriving has been exceptional.

Felix's xA per 90 of 0.41 at Villa is the highest of any midfielder in the Premier League over the same period. He's created 14 chances in six appearances, including three assists, and his ability to receive the ball in tight spaces and pick out runs from Ollie Watkins and Jhon Duran has added a dimension Villa were missing.

The defensive side of his game remains a work in progress -- his pressing numbers are below the team average -- but Emery has shielded him from defensive responsibilities by deploying him in a free role behind the striker with two industrious midfielders doing the dirty work behind him.

Villa's points per game since Felix's arrival: 2.33, up from 1.82 before. It's a small sample, but the trend is clear.

Verdict: Looks like the move he needed. Early days, but the signs are excellent.

Amad Diallo's Loan to Napoli

Manchester United's decision to loan Amad Diallo to Napoli for the second half of the season raised questions about their squad planning, but it's been brilliant for the player. In Serie A, Diallo has thrived as a right winger in Italiano's 4-3-3, using his dribbling ability and pace to devastating effect.

His xG per 90 of 0.38 and xA per 90 of 0.29 since arriving are both career-best figures. He's scored three goals and assisted two in seven appearances, and his pressing numbers (12.4 pressures per 90 in the final third) are among the highest in the league.

Napoli's right flank was a weakness before Diallo's arrival. Since he came in, their xG from attacks down the right has increased by 31%. That's a significant tactical improvement that has coincided with Napoli moving up from fourth to second in the table.

Verdict: The best loan move of the window. United might regret letting him go.

The Steady Contributors

Carlos Soler to West Ham

West Ham's midfield needed reinforcement, and the Spain international from PSG has provided exactly that. Soler's impact has been more about defensive structure than attacking output -- West Ham's xG conceded per game has dropped from 1.62 to 1.31 since his arrival.

His passing range from deep has also improved West Ham's build-up play. Their progressive passes per game are up 15% with Soler in the side. He's not going to make the headlines, but he's made West Ham harder to beat, which is exactly what Julen Lopetegui needed.

Verdict: Solid, unglamorous, effective. The definition of a sensible January signing.

Bryan Mbeumo to Chelsea

Chelsea's decision to sign Mbeumo from Brentford for a reported 45 million drew criticism about overpaying for a player from a smaller club. But the early evidence suggests he's adapted to the step up in quality without issue.

His xG + xA per 90 of 0.54 is marginally lower than his Brentford numbers (0.61), but that's to be expected as he adjusts to new teammates and a different system. His pressing intensity has been impressive, and his versatility across the front line has given the Chelsea manager tactical flexibility.

The concern is that Chelsea already had too many attackers. Mbeumo is competing with Palmer, Nkunku, Madueke, and others for playing time, and whether he'll get enough minutes to justify the fee remains to be seen.

Verdict: Good player, questionable squad planning. The talent is there, but Chelsea's bloated squad might limit his impact.

The Jury's Still Out

Randal Kolo Muani to Juventus (loan)

The French striker arrived from PSG on loan with high expectations, but his integration has been slow. He's started four games and come off the bench in three more, scoring once, and his xG per 90 of 0.31 is decent without being spectacular.

The issue is system fit. Motta's patient build-up play requires a striker who can drop deep and link play, but Kolo Muani's best work comes when he can run in behind defences. There's a mismatch between what the team needs and what the player provides.

That said, January signings often take time to settle. Kolo Muani's movement and pace are genuine assets, and as he builds an understanding with his new teammates, the output could improve significantly.

Verdict: Too early to judge. The talent is obvious, but the system fit is uncertain.

Dominik Szoboszlai to Real Betis (loan)

Liverpool's decision to loan out Szoboszlai was a sign that Slot's midfield hierarchy was set. At Betis, the Hungarian has had more regular minutes but hasn't yet produced the kind of performances that suggest he was being underused at Anfield.

His xG + xA per 90 of 0.32 at Betis is actually lower than his Liverpool figure (0.39), though the quality of teammates around him is obviously different. His pressing numbers remain high, and he's been used in a variety of positions, which may be hindering his rhythm.

Verdict: Needs more time. The move makes sense for all parties, but the results haven't arrived yet.

The Misses

Andre Onana to Al-Hilal... and Back?

This wasn't technically a January transfer, but Onana's saga deserves mention. After being sold to Al-Hilal in January, the goalkeeper reportedly regretted his decision within weeks and has been linked with a return to European football. His replacement at United has been functional but unspectacular.

The lesson: sometimes the grass isn't greener, even when it comes with a massive pay rise.

What the Data Tells Us About January Transfers

Looking at the broader pattern of this window, a few trends emerge:

Loan moves outperformed permanent signings. Players who arrived on loan (Diallo, Kolo Muani, Szoboszlai) integrated faster than those who made permanent moves, possibly because the pressure of a big transfer fee affects early performances.

System fit matters more than individual quality. Trossard and Felix have thrived because they've joined teams whose tactical systems suit their strengths. Kolo Muani's struggles at Juventus show what happens when the fit isn't right.

Defensive contributions are underrated. Soler's impact at West Ham and Trossard's pressing at Atletico show that the most valuable January signings aren't always the ones scoring goals. Improving a team's defensive structure can be just as transformative.

Small sample sizes demand caution. We're working with six to eight games of data here. That's enough to identify trends but not enough to draw definitive conclusions. Ask us again in May, and this ranking might look very different.

The January window is a gamble. Always has been, always will be. But this year's crop of signings has produced some genuine success stories, and the data suggests a few more are on the way.