The Austria international had a late night yesterday, arriving from Germany to seal his beat-the-deadline loan switch from Bundesliga giants Bayern Munich.
He was in the stands cheering his new team-mates on as Erik ten Hag's Reds look to seal a place at Wembley, by completing the job against Forest, following a 3-0 first leg triumph at The City Ground.
The midfielder, who will hope to be available for Saturday's Premier League home game with Crystal Palace, sat in the row in front of former United men Andy Ritchie and Denis Irwin, and got a close look at Erik ten Hag's side in action.