Paul Pogba, Eric Bailly, Chris Smalling and Phil Jones all trained with their Manchester United team-mates ahead of vital clashes against Celta Vigo and Arsenal.
Bailly and Luke Shaw were the latest to join United's lengthy injury list when they were both forced off during Sunday's 1-1 draw with Swansea.
Shaw's foot injury could well end his season but key defender Bailly, who limped off in the 61st minute, does not appear to have suffered any lasting damage.
Neither Smalling nor Jones have featured for United since picking up knee and toe injuries respectively on England duty in mid-March.
United boss Jose Mourinho has been critical of both for not making themselves available sooner and had said he did not expect either to be fit for the first leg of the Europa League semi-final against Celta in Spain, with a crucial Premier League trip to Arsenal to follow three days later.
Mourinho had been faced with the prospect of having to either play Michael Carrick in the centre of defence or teenager Axel Tuanzebe.
But it now looks as though he will have more options at his disposal, while Pogba's return after missing the last two matches is more welcome news.
Playmaker Juan Mata could make his first appearance since groin surgery and Marouane Fellaini, who is serving a three-match domestic ban, also comes into contention in Europe.
United remain without a number of first-team players, however, with Zlatan Ibrahimovic, Marcos Rojo and Timothy Fosu-Mensah joining Shaw on the sidelines.
