Christian Ziege, Kasey Keller, Jamie Redknapp and Milenko Acimovic have been added to the 'doubtful' list since Saturday's defeat to Middlesbrough, with Ziege more of a 'certainty' to miss out against Cardiff.
Glenn was asked if any of the players approaching fitness could be drafted in on Tuesday.
"This is the problem," pondered Glenn. "Do you risk someone taking a step backwards for a while?
"I don't know, I need to talk to players. I've seen what training they've had and it would be a risk. Decisions will be made by Tuesday.
"We're scheduling players on their comebacks and we know where they're at.
"Steffen Freund played in a reserve game last week and he could be a player that might feature, but again that would be a risk."
Alternatives available to Glenn include young midfielders Jonathan Blondel and Rohan Ricketts.
"We might have to change it and it might involve playing some younger players, who knows? We've got to dig in deep and get on with things.
"It would be asking a lot of them. It would be a good experience for them and they might just go in and play with a different mentality to the current team."
Glenn says that, of the injured players, only Steffen Freund could come into contention for a place against Cardiff - but it would still be a risk.