"David was excellent [in Cluj]," said Ferguson. "He's an outstanding goalkeeper who is getting better all the time.
"I don't know whether I should play him on Sunday or not. The way we've been doing it in the last few weeks [rotating between the duo] has worked quite well for us really.
"I think everybody wants to play and goalkeepers are no different. But the way I look at it, at the moment, is giving the two of them experience will help them in the long term."
Ferguson added that he will continue to rotate the two goalkeepers until one of them shows signs of dominance.
"Obviously, at some stage, one of them will take over if he shows real consistency, top-level performance and maturity," said the 70-year-old.
"At the moment, neither has got that big-game experience but they will get that in time. I'm not setting any targets [in terms of a time-frame for that to happen]."
United are currently third in the Premier League table with 12 points from six matches, four points behind leaders Chelsea.