The Villans striker suffered a setback in training last week and missed the 1-0 Premier League win over Sunderland last weekend.
The problem relates to Bent's right ankle, the same one he injured last season which forced him out of the final three months of the last campaign and ended his hopes of being part of England's Euro 2012 squad.
And Villa boss Lambert claims he’s put no timescale on a return to the first-team for the Three Lions striker.
"Darren had a scan on Wednesday and it's still too early so we will have to go with the same squad of players," he said.
Asked how long Bent would be out, the Scot added: "Darren's doing okay at the minute but we'll have to wait and see. It is the ankle he injured against Wigan (last season) so we will wait and see."
Lambert confirmed Bent was not fit enough to even be a substitute against the Red Devils, adding: "It is not right at the moment."