Speaking after the unveiling of Japanese international Kazuyuki Toda, the boss said that his quest to recruit a striker is an ongoing one that he hopes will draw to a positive conclusion.
"I'm hoping so, we're working away and there is more work to be done," said Glenn.
"We are working exceedingly hard at the moment - like a lot of clubs are. It's very difficult out there, I keep saying it, but it really is. The game has changed.
"You would have thought there would have been a lot of activity in this window, but there is not much happening.
"We're running out of time and it is a close call. We're delighted to get one player in - two would be smashing and would give everyone a lift."
Glenn had little to add to reports that Tim Sherwood was preparing to undergo a medical at Portsmouth today and confirmed that Sergei Rebrov's loan switch to Fenerbahce is on the verge of completion.
"I can't take it much further on Tim Sherwood than has already been said. He's got a couple of options and we'll soon know if they have been taken up.
"Sergei is out in Turkey and has passed a medical. There are still a few minor details to be ironed out. It is a 12-month loan."
Meanwhile, Glenn paid tribute to the professionalism of Rebrov and said he was surprised by comments made by the striker in a Sunday newspaper.
"All I can say is that Sergei has been a terrific professional.
"I have the utmost respect for Sergei - it has been difficult for him. I feel I've given him opportunities and perhaps he hasn't taken them. Perhaps he feels he has - I don't know.
"I was always open and honest with him. He had personal issues to deal with and I allowed him to return to the Ukraine on many, many occasions.
"I was surprised with his comments, but I respect him. His attitude in training during a difficult time for him was very professional and I have a lot of admiration for him.
"He will do well. I wished him all the best and sincerely hope he settles in Turkey and plays exceedingly well. There is a player waiting to come out and it just hasn't worked here. That's the truth of the matter."
Glenn confirmed that he is hoping to bring in another new face during the final days of the transfer window, but admits it will be a 'close call'.