"Our only concern at the moment, and it is a big concern, is the fitness of Defoe," says Glenn.
"We had to withdraw him from the under-21s and his groin is only responding slowly to the treatment and rest he is having.
"It is a case of fingers crossed that he will be okay for the Sunderland game."
Of the striker situation overall, he admits: "It is the one department in the squad where we are down on numbers; last year we got away with it with Paolo, Fredi, Jermain, and Paul Kitson when Titi wasn't fit, but it is painfully thin just operating with four, which includes Titi this year.
"Most Premiership clubs operate with more than four strikers.
"Last year we coped but this year it hasn't gone so well for us.
"Without doubt we are looking at this area; since September 1st scouting activity has not been at its highest but we are starting to pick the reins up now - and we have got specific targets to look at in the next transfer window."
Trevor Sinclair, who can also operate as a striker, is also on the injured list having withdrawn from the England squad, and Paolo Di Canio has a foot problem.
"Trevor is coming on fine; the toe has been badly bruised but I am sure Monday he will start jogging and Tuesday he will be working hard at the training ground, ready for football next Wednesday and Thursday," says Glenn.
"I am not expecting any problems with him playing at Sunderland.
"Paolo has been back to the centre in Bologna to have more treatment on his foot to get him 100% for the Sunderland game.
"The important thing is, come the game at the Stadium of Light, that we have Fredi fit, Jermain fit, Paolo will be no problem, and Titi, who is also away playing for Guinea, returning okay.
"The only problems I want are of team selection.