Cape Town - Manchester United boss Ole Gunnar Solskjaer could be without four first-team players for Wednesday's meeting with Barcelona.
The Red Devils could be without Nemanja Matic, Ander Herrera, Eric Bailly and Antonio Valencia, with the quartet all missing training on Tuesday ahead of Wednesday's Champions League tie.
Former Arsenal forward Alexis Sanchez was back with the group after recovering from a knee problem, while striker Marcus Rashford was involved in the session after missing the game against Wolves last week with an ankle issue.
Solskjaer has hinted that Rashford could play some part of the game but United fans face an anxious wait over the other injured stars.
While United's medical room is full, Barcelona will travel to Old Trafford with just one confirmed absentee.
Midfielder Rafinha is out due to a knee problem, while winger Ousmane Dembele will have to pass a late fitness test after suffering an injury in the last European game against Lyon.
Lionel Messi, Philippe Coutinho and fit-again striker Luis Suarez were used up top against Atletico Madrid last weekend and they should all retain their places for the trip to England for Wednesday's quarter-final first leg.
The Spanish outfit have never won at Old Trafford, but they did win the last meeting between the pair in 2011, when they were victorious 3-1 at Wembley to lift the trophy.
Solskjaer's troops managed to pull off a shock victory last time out as they beat Paris Saint-Germain on a historic night at the Parc des Princes, but they have struggled for form of late.
Barcelona are cruising to an eighth La Liga title in 11 years and Ernesto Valverde's men are unbeaten in their last six matches in all competitions.
Kick-off is at 21:00 (SA time).