Here is the essential team news you need to know ahead of the last 16 first leg clash in Greece.
Javier Saviola - Argentine striker has 24 goals this season for the Greek side, but will miss the game against United. He went off at the weekend injured after just 33 minutes with a thigh injury against OFI Crete.
Nelson Valdez - The Paraguayan forward was brought in on loan, but is a doubt for the fixture also with a thigh injury. Olympiakos remain hopeful he will play, with their coach particularly secretive over his status in a pre-match press conference.
Marko Scepovic - Serbian striker Scepovic netted a hat-trick at the weekend but fate is smiling on United: He is cup-tied and unable to play after featuring for Partizan Belgrade earlier in the season.
Rafael da Silva - Rafael hasn't played since being taken off with concussion sustained in a collision with Olivier Giroud against Arsenal. He has travelled with United and is available for selection at right-back.
Phil Jones - David Moyes has confirmed that England international Phil Jones has not travelled to Greece, with a hip problem meaning he hasn't played since the loss to Stoke City.
Jonny Evans - Another victim of the loss at the Britannia, Evans still has a calf problem which caused him to play just 11 minutes of that game. He also has remained at home.
Nani - Portuguese winger Nani is still sidelined with a hamstring injury and has also been left behind. There remains no word on a possible comeback date.
Danny Welbeck - United do have good news in the form of Danny Welbeck who has shaken off a knee injury and is fit and ready to feature.
Juan Mata - United's record signing is cup tied after playing for Chelsea earlier in the competition, and has not made the trip to Greece.
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