Marcos Rojo suffered a possible injury setback on his return to action with Manchester United's Under-23 side on Friday.
Argentina defender Rojo's last competitive action came in his country's 4-3 defeat to France in the last-16 of the World Cup.
United boss Jose Mourinho told reporters earlier in the day that he hoped Rojo and close-season signing Diogo Dalot would be able to complete 90 minutes and show they are ready for first-team selection.
However, Rojo limped off after 54 minutes of the 1-1 draw against Reading.
United Under-23s boss Ricky Sbragia later told MUTV Rojo would be "okay" after spending time with the club's medical staff.
Dalot played for the entirety of the contest as United's Joshua Bohui cancelled out Ben House's early opener for the visitors.
United's defence has come under some scrutiny this season following their indifferent start to the campaign.
Mourinho's side have conceded seven goals in their opening four Premier League matches, including three in each of the defeats to Brighton and Tottenham.
Ander Herrera lined up on the right-hand side of a back three against Spurs - a potential message from Mourinho after the club's failure to land a new centre-back over the summer.
The former Chelsea boss' shortlist included the likes of Toby Alderweireld, Harry Maguire and Diego Godin, but Dalot proved to be the only defensive acquisition during the off-season.
That leaves Rojo, Eric Bailly, Chris Smalling, Phil Jones and Victor Lindelof as the senior centre-backs available to the Old Trafford outfit.