Rufus went off against Sheffield United with an ankle injury on Saturday, and Glenn says: "He is having more scans today and hopefully in the evening we should know - but he is sore at the moment.
"It was hugely disappointing for us and Brevett that he went off after 29 minutes. He is a tough boy and he wouldn't have gone off unless he was hurt.
"And up to that time Kevin Horlock hadn't given the ball away. You could already see that he is an experienced player coming from a passing team in which he was comfortable.
"It was just a shame that he had to drop to left back but he coped very well, used his versatility, and showed his experience."
Glenn knows he will have to ask his players to play in various positions this campaign, and adds: "Repka, Dailly, Horlock, Lomas...there are four or five players that, when fit, are versatile.
"They are good people who don't mind playing out of their favourite position, to shift around for the good of the team.
"You get a lot of players that pigeon hole themselves, saying 'I am this position' and won't try another position.
"It was good to see Tomas Repka filling at right back and considering he wasn't told he was starting there until Friday morning, and had only one practice, I thought he coped very well.
"He has certainly given me a lot of food for thought about him playing at right back at other times this year, which he is positive about doing."
As for other injuries, he adds: "Sofiane has got a groin injury again and we can't specifically say when Michael Carrick will be back."