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.