Well if you don't think they can get a clean sheet then they need at least 4 goals.
Haven't scored more than 3 goals in a match since the 5-0 win at Leverkusen in late November. Can't see it happening if we play Carrick + Cleverley in midfield as neither of them links midfield with attack.
Smalling and Evans are both injured, so at centreback it's 2 out of Vidic, Ferdinand and Jones. Considering Vidic-Ferdinand played in Greece and Vidic-Jones both gave away penalties on Sunday, it doesn't fill me with confidence in our ability to keep a clean sheet.
Rooney and Van Persie have been disappointing in recent weeks, Welbeck's done well recently but if he plays it'll probably be on the left. Kagawa will play some part in this match, I imagine he'll come off the bench if we need a goal or 2 in the last 15 minutes.
Olympiakos aren't a great team, and they've lost 2 of their last 3 matches but they just tied up the Greek League on the weekend, they're putting all their eggs into this basket. Confidence is extremely low at United right now, unless Olympiakos completely shit their pants tonight, United are going out.