The striker sustained ligament damage after falling awkwardly attempting a shot on goal in Ireland's friendly against Australia on Tuesday night.
"At the moment we can say that he'll definitely be out for two weeks," said Glenn at his pre-Leeds press conference.
"He's had scans and what we'll do is have more observations further down the line when the swelling has gone down.
"I would say he's out of our next three games and the following internationals.
"It's an ankle ligament strain but at this moment we need to let it settle. We're hoping it's not going to be long term but at this stage it's at least two weeks."
Glenn Hoddle has revealed this morning that Robbie Keane will be out for at least two weeks with his ankle injury.