Gary Neville explained his theory why Adnan Januzaj was not selected to start against Olympiakos.
The teenager started against Liverpool at the weekend but like teammates Mata, Rooney and Van Persie, was ineffective in the 3-0 loss.
David Moyes left him out completely in the first leg, this time United's number 44 did make the bench, but was once again an unused substitute.
Former United man Gary Neville has his own theory about why that was, and believes the internationally-coveted prospect is facing burnout.
Neville told SkySports: "Januzaj looks shot."
"He's a young player who has played a lot. He looks like he needs a break."
The 19-year-old has played 25 Premier League and Champions League games in his debut season, including 14 starts.
What he has achieved this season already has been magnificent, and if he truly is exhausted then a spell out of the first team may not be a bad move for him.
Liverpool boss Brendan Rodgers did the same with Raheem Sterling in the second half of last season, and it has paid off with the youngster coming back even better this campaign.
Neville's assessment is just his personal viewpoint, and David Moyes could have simply omitted Januzaj for tactical reasons - but the theory is certainly a credible one and it may be we see less and less of him as the season draws to a close.