Second placed United could be without the attacking threats of Anthony Martial, Marcus Rashford and Mason Greenwood who are all hoping to be fit in time to face Graham Potter's Brighton.
Martial missed training on Friday with a reported knee issue picked up on France duty, while Rashford and Greenwood’s pulled out of their England squads.
Victor Lindelof also missed training with an ongoing back complaint, while Ole Gunnar Solskjaer refused to confirm whether David De Gea or Dean Henderson will start in goal on Sunday.
Scroll down and click through to see who is struggling to be fit for Sunday and when they can be expected to return.
1. Juan Mata
Unspecified injury. The Spanish midfielder almost made it back before the international break and could be available for selection for Brighton. Solskjaer said: "Maybe, but I'm not sure. It is taking a little bit longer than we expected."
2. Marcus Rashford
Foot injury. Trained in the week and could be available for selection. "They [Marcus and Mason] both joined this morning and hopefully they don't get any reaction. If they complete the session tomorrow they'll be available for selection," Solskjaer said.
3. Mason Greenwood
Unspecified injury. Greenwood will be assessed ahead of Brighton. Trained this week and in contention. "If they complete the session tomorrow they'll be available for selection," said Solskjaer.
4. Anthony Martial
Knee injury. Has a chance but looking doubtful for Brighton. Solskjaer said: "Neither of them [Anthony nor Victor] trained this morning. We are still waiting for final confirmation on how they are."