While Milan have faltered, the Viola are still pursuing Italy's top four despite their own autumn woes, sitting just three points behind their hosts with nearly a third of the season played.
Match preview
Milan may have been more pleased than most when international football intervened earlier this month, as one good Champions League result aside, they had been tail-spinning from the summit of Serie A and back towards the chasing pack.
Juventus and city rivals Inter Milan pulled clear at the top of the standings, as Stefano Pioli's injury-hit squad suffered a series of setbacks that have partly undone their superb start to the 2023-24 season.
Just days after a crucial defeat of Paris Saint-Germain in Europe, Milan returned to domestic duty for their final fixture before the international break down at Lecce's Stadio Via del Mare, and having previously lost to Juventus and Udinese either side of a 2-2 draw with Napoli, the Rossoneri were on course for success when Olivier Giroud and Tijjani Reijnders struck before the break.
However, a second-half collapse saw them pick up only one point in the end, and only the VAR's controversial intervention denied Lecce a memorable winner deep into stoppage time.
Spoiling his 100th Milan appearance, Giroud was sent off late on, adding to Pioli's selection problems at a time when the former Fiorentina boss is seriously short of numbers in defence and up front.
Now with one eye on their Champions League clash with Borussia Dortmund next Tuesday - which could ultimately decide who goes through to the knockout phase - Milan must host a dangerous opponent in Serie A. Suffering three home losses in a row would be unacceptable for the Rossoneri's demanding owners, so defeat to Fiorentina is not an option.
While Milan's malaise makes them more vulnerable at the moment, Fiorentina will have to overturn recent precedent if they are to take three points back to Florence this weekend, having lost each of the teams' last three league meetings at San Siro.
The Viola bounced back from three consecutive Serie A defeats last time out, when they saw off in-form Bologna at Stadio Artemio Franchi thanks to goals from Giacomo Bonaventura and Nicolas Gonzalez - perhaps their two most effective players this season.
A much-welcomed victory on home soil came days after Vincenzo Italiano's side returned to winning ways in Serbia, with a 1-0 defeat of Europa Conference League opponents Cukaricki leaving them in good shape to progress from Group F.
Last term's beaten finalists will host Genk next week, when a win would be enough to go through, but first they aim to continue the upswing that followed a worrying domestic downturn.
Before beating Bologna, Fiorentina had lost three Serie A matches on the spin without scoring - the same number of goalless games recorded in their previous 27 - and the Viola's strikers have yet to convince since arriving in Tuscany; leaving Gonzalez and Bonaventura to pick up the slack.
AC Milan Serie A form:
W
W
L
D
L
D
AC Milan form (all competitions):
L
L
D
L
W
D
Fiorentina Serie A form:
W
W
L
L
L
W
Fiorentina form (all competitions):
L
W
L
L
W
W
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Team News
Having sustained a hamstring injury on Switzerland duty, Noah Okafor has joined a growing list of absentees from Milan's multinational squad, and coach Stefano Pioli will also be without first-choice forwards Rafael Leao (thigh) and Olivier Giroud (suspended) on Saturday evening.
Summer signings Luka Jovic and Samu Chukwueze are yet to make any impact at San Siro, but both could therefore be asked to step into a front three also featuring Christian Pulisic.
Fikayo Tomori and Malick Thiaw will be paired at the heart of the hosts' back four, as Simon Kjaer, Pierre Kalulu and Marco Pellegrino are all sidelined as well.
There is some better news for the Rossoneri in midfield, as Ruben Loftus-Cheek - who excelled against PSG, but last appeared in Serie A nearly two months ago - should return after overcoming muscular fatigue and an illness.
Fiorentina, meanwhile, will be missing Luca Ranieri due to a one-match ban for accumulated bookings; however, young full-back Michael Kayode is close to completing his comeback from an ankle injury.
Dodo and Gaetano Castrovilli are not due back in action until 2024, but Vincenzo Italiano should have an otherwise full squad to select from, so M'Bala Nzola and Lucas Beltran will battle it out to occupy the Viola's centre-forward role.
Starting behind either striker, Giacomo Bonaventura - who scored 30 goals from 155 Serie A appearances for Milan - has netted five times this season, already equalling last season's total. The Italy midfielder last fared better back in 2017-18, with a final tally of eight for the Rossoneri.
AC Milan possible starting lineup:
Maignan; Calabria, Tomori, Thiaw, Hernandez; Loftus-Cheek, Krunic, Reijnders; Chukwueze, Jovic, Pulisic
Fiorentina possible starting lineup:
Terracciano; Parisi, Milenkovic, Martinez Quarta, Biraghi; Arthur, Duncan; Gonzalez, Bonaventura, Brekalo; Nzola