United's loan midfielder Lee Martin is to have a knee injury assessed by club's medical staff.
The 19-year-old winger, who is currently enjoying a spell with Rangers, has been struggling with the injury for three weeks now, and could miss next week's Uefa Cup trip to Livorno.
"He has been troubled by this for three weeks after taking a knock on his knee and I am little bit worried," Rangers boss Paul Le Guen told the club's website.
"Our doctor will work in conjunction with Manchester United."
Rangers are already without injured wingers Chris Burke and Libor Sionko for the Uefa Cup group stage opener in Italy.
"It does leave us short of wingers," Le Guen added. "It is bad luck, but we must keep our head up and keep working."
Martin isn't the only United loanee recuperating at Carrington, team-mate Adam Eckersley has also returned from his spell with Brondby after tearing a hamstring.
Boss Rene Meulensteen told ManUtd.com: "I was pleased that Adam could come on loan to us but because of injury he was only able to play one full league game.
"He has now a tear in his hamstring which will keep him out for several weeks, and that's a shame because he enjoyed his stay with Brondby.
"I hope there will still be an opportunity for Adam to come and play for us."