The dynamic wing made six appearances for the Lions and scored five tries throughout his debut tour, including an interception effort in the historic third-Test triumph in Johannesburg.
But the electric-wing will now be out of action until December after undergoing surgery on a toe injury.
That rules 13-times capped Monye out of England's autumn internationals and keeps him out of action for Harlequins for the first half of the season.
He could miss up to nine of the next Aviva Premiership matches and is certain to miss the first two rounds of the Amlin Challenge Cup against Bayonne and I Cavalieri Estra before facing a race against time to be fit for the European double-header against Connacht in December.
But while the news comes as a big blow to Monye, Quins and England, his club have confirmed that the surgery was a success and they are hopeful of a full and quick recovery.
"The extent and duration of the injury will be known more clearly after further consultation with the surgeon, and further updates will be given," said a Quins statement.