Should the injury prove to be serious, it could take Gibson off the pitch for at least four weeks.
Aston Villa and Blackburn Rovers had both showed interest in the midfielder, with the latter making a bid of £3.5 million.
After a trip to the hospital on Thursday Gibson now has a protective cast on his right foot. He has to wait for the swelling to subside before an x-ray can determine the nature and seriouness of his injury.
Sir Alex Ferguson had struck the 23-year-old off his plans and Gibson has been looking to join another club after a deal with Sunderland fell through. The Irish international was omitted from United's pre-season tour in the United States, and has yet to make the first-team squad this season.
While United will persist in trying to strike a deal before the end of the transfer window, the club now faces the problem of Gibson's injury deterring potential interest.