The Rossoneri's downturn reached a new nadir last time out, as they followed Supercoppa failure with a 4-0 thumping at Lazio; meanwhile, their visitors' start to 2023 has been even worse, and they sit just one place above the relegation zone.
Match preview
Already distanced from top spot nearing the midpoint of their Scudetto defence, Milan slipped further behind in the title race on Tuesday, when they suffered a second heavy defeat in the space of six days.
The champions seemed bereft of confidence in Rome, as Lazio's Sergej Milinkovic-Savic set the home side on their way after just four minutes, and the Rossoneri were picked off again and again by Maurizio Sarri's men, who were without captain Ciro Immobile.
Having conceded four goals without scoring in a league match for the first time since December 2019, Stefano Pioli's losing return to his former club leaves the Rossoneri 12 points adrift of Serie A leaders Napoli at the halfway stage.
A winless run of five matches in all competitions - including a bitter 3-0 defeat to arch-rivals Inter in the Supercoppa Italiana - has not only allowed Lazio to close within one point but also dragged in-form Atalanta and Roma back into the top-four race.
Also out of the Coppa Italia after an extra-time loss to Torino earlier this month, Milan's faltering backline has started to splinter - with 12 goals conceded in that win-free streak - and their none of their summer signings have made an impact at San Siro as yet.
With another Milan derby and a Champions League tie against Tottenham Hotspur looming ever closer on the radar, Pioli will be eager to get back on track as soon as possible - and the first opportunity comes in Sunday's early kickoff.
Sassuolo's goalless draw with Milan last August continued a relatively successful spell against their second-city counterparts, as they have also won both of their last two meetings with the Rossoneri at San Siro.
More recently, though, Alessio Dionisi's side have recorded two draws and six defeats from their last eight league games, and only once before have the Emilian club gone nine in a row without winning in Serie A - between December 2017 and March 2018.
Despite taking an early lead through Gian Marco Ferrari's close-range finish, they were forced to settle for a single point last week, as a Monza side which has moved above them in the standings struck back in the second half.
As a result, since Dionisi took the reins from Roberto De Zerbi in mid-2021, Sassuolo have let 34 points slip after holding a winning position - during that time, only Verona and Bologna have dropped more when ahead in Serie A.
That is surely a cause for concern, and such profligacy has played its part in the Neroverdi's slide to 17th. Since September, they have failed to win a single away game, too, so taking advantage of Milan's malaise may be easier said than done.
AC Milan Serie A form:
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W
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AC Milan form (all competitions):
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Sassuolo Serie A form:
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Sassuolo form (all competitions):
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Team News
After Fikayo Tomori limped off midway through the first half of Milan's loss to Lazio, to be replaced by his former centre-back partner Simon Kjaer, the latter should join Pierre Kalulu at the heart of the hosts' defence on Sunday.
Ismael Bennacer is also unavailable - in his case, due to suspension - with Alessandro Florenzi, Zlatan Ibrahimovic and much-missed goalkeeper Mike Maignan still sidelined by injury.
In better news for Stefano Pioli, full-backs Theo Hernandez and Fode Ballo-Toure returned to training in midweek, while captain Davide Calabria appears to have shaken off a calf problem and should start at right-back.
Misfiring big-money buy Charles De Ketelaere will hope for promotion to the lineup after another quiet showing from Brahim Diaz at the Olimpico, Rade Krunic could cover for Bennacer in midfield, and Olivier Giroud features up front despite failing to score in his last five league matches: the French forward has never endured a longer goalless streak in Serie A.
Meanwhile, Sassuolo will be without goalkeeper Andrea Consigli and on-loan Inter striker Andrea Pinamonti through injury, while Rogerio's participation is in some doubt due to a shoulder issue.
In the visitors' attack, Pinamonti's absence will mean another opportunity for Agustin Alvarez or Gregoire Defrel to lead the line.
Either man should be flanked by Domenico Berardi - who has been directly involved in 14 league goals against Milan over the years - and Armand Lauriente.
AC Milan possible starting lineup:
Tatarusanu; Calabria, Kalulu, Kjaer, Hernandez; Tonali, Krunic; Saelemaekers, Diaz, Leao; Giroud
Sassuolo possible starting lineup:
Pegolo; Toljan, Erlic, Ferrari, Rogerio; Frattesi, Lopez; Berardi, Traore, Lauriente; Alvarez