Graham Potter's side sit dead last in the section after two matches without a win, while the Rossoneri have taken four points from six to occupy first place.
Match preview
The script had already been written before the game, and Conor Gallagher stepped up to the role. With Potter finally taking charge of a Premier League match for Chelsea, his side ran out 2-1 winners over Crystal Palace thanks to a peach from the ex-Eagles loanee.
Odsonne Edouard's seventh-minute put Palace in the ascendancy, but Pierre-Emerick Aubameyang's well-taken first goal for Chelsea restored parity for the visitors before Gallagher came off the bench to curl home a wonderful winner in the dying embers.
Having got off the mark domestically, ending Chelsea's winless run in Europe is next on the agenda for Potter, whose first game in charge of the club ended in a 1-1 stalemate with Red Bull Salzburg after the final nail in Thomas Tuchel's coffin was hammered in with the 1-0 defeat to Dinamo Zagreb.
As things stand, Chelsea sit rock bottom of Group E with just one point to their name, but first-placed Milan are only three points clear at this early stage of proceedings, and the Blues will be intent on upsetting the apple cart on Wednesday.
Not since March 2010 have Chelsea suffered defeat at home to Italian opposition in Europe - losing 1-0 to Jose Mourinho's Inter Milan - and the hosts have gone eight games at Stamford Bridge without defeat, but they have also failed to keep a clean sheet in as many matches in all competitions.
The injury crisis in Stefano Pioli's ranks went from bad to worse during AC Milan's Serie A clash with Empoli at the weekend, but the Scudetto holders still ran out comfortable victors as they continue to play catch-up in the battle to defend their Serie A title.
Fode Ballo-Toure, Rafael Leao and Ante Rebic were all on target as the Rossoneri returned to winning ways in comprehensive fashion, and some may consider Wednesday's game to be an audition for Leao, who has been strongly linked with a switch to Chelsea in recent months.
Since a reported late approach from the Blues failed, the 23-year-old has led the Rossoneri revolution to help his side to fourth place in the Serie A table at present, although Atalanta BC and Napoli are three points clear in the top two podium positions.
Pioli has witnessed his side draw with Salzburg and overcame Zagreb to occupy top spot in Champions League Group E, and similarly to Chelsea, the Italian champions have also demonstrated some defensive deficiencies in recent weeks - conceding in six straight games in all tournaments.
However, Milan have gone eight away games without defeat and are now aiming to end a European hoodoo on English turf, with their only win in such matches coming at Old Trafford against Manchester United in February 2005.
The Rossoneri have otherwise come away with seven draws and 12 defeats from their other 19 trips to face English clubs in continental competition, and they have not taken on Chelsea since the 1999-2000 Champions League group stage, with both games ending level.
Chelsea Champions League form:
L
D
Chelsea form (all competitions):
W
L
W
L
D
W
AC Milan Champions League form:
D
W
AC Milan form (all competitions):
W
D
W
W
L
W
Team News
Chelsea are already expected to make do without Edouard Mendy (knee) and N'Golo Kante (thigh) for the visit of Milan, while Marc Cucurella and Carney Chukwuemeka will both need assessing after missing the win over Palace due to illness.
Cucurella has reportedly been hospitalized with his infection, so it is difficult to see the left-back making himself available for Wednesday, while Jorginho sustained a knock at Selhurst Park and has also emerged as a doubt for the contest with the Rossoneri.
Gallagher could therefore be rewarded for his game-winning exploits with a start in the Champions League if Jorginho cannot recover in time, while Thiago Silva - who was fortunate not to see red at the weekend - should join Wesley Fofana at the back again.
Chelsea's treatment room is well-occupied, but Milan's medical resources are being stretched to the limit, as Theo Hernandez, Mike Maignan, Zlatan Ibrahimovic, Divock Origi, Junior Messias and Alessandro Florenzi are all confined to the infirmary.
Pioli also witnessed all of Simon Kjaer, Alexis Saelemaekers and Davide Calabria come off injured in the win over Empoli; the two defenders both sustained hamstring issues while Saelemaekers suffered a sprain to the knee.
The severity of the trio's issues is currently unclear, but Pioli will likely be required to rejig his starting XI once again, as Sergino Dest, Rade Krunic and Pierre Kalulu prepare to be drafted into the first XI.
With Ibrahimovic and Origi absent, the attacking responsibility will fall onto the shoulders of Olivier Giroud, who scored 39 goals in 119 appearances during his time at Chelsea, and Fikayo Tomori will also have a point to prove to his former employers.
Chelsea possible starting lineup:
Kepa; James, Fofana, Silva, Chilwell; Mount, Kovacic, Gallagher; Havertz; Aubameyang, Sterling
AC Milan possible starting lineup:
Tatarusanu; Dest, Kalulu, Tomori, Ballo-Toure; Tonali, Bennacer; Krunic, De Ketelaere, Leao; Giroud
We say: Chelsea 1-1 AC Milan
Milan's lengthy injury list will have the home crowd travelling to Stamford Bridge with plenty of optimism, but Pioli is still packed with quality options in all areas of the field, including two former Blues determined to make an impact upon their return to the capital.