The Sweden forward, who played for United from 2016-18, has missed Milan's past four matches with a left thigh injury. That ruled him out of a return to Old Trafford, where Milan snatched a 1-1 draw in the first leg of the round of 16.
Milan coach Stefano Pioli said Wednesday that Ibrahimovic has recovered sufficiently to play some part in Thursday's match but would not confirm whether the 39-year-old Ibrahimovic would be part of the starting lineup.
"We'll see what choices I'll make tomorrow,'' Pioli said. "His return to the squad is important for us but clearly he won't be able to play for 90 minutes.''
Milan have won only one of the four matches during Ibrahimovic's absence and has slipped nine points behind Serie A leader Inter Milan.
It was a fourth spell on the sidelines for Ibrahimovic this season after testing positive for the coronavirus and two other injuries to his left leg. Ibrahimovic has nevertheless scored 14 goals in as many league matches.