The Daily Mail says Bent has been out of the first team for the past month, with manager Lambert claiming the striker had problems with his ankle. But it appears he has been fit to play for the past three weeks.
Intriguingly, Sunderland will receive another seven-figure instalment if Bent reaches 50 games for the club. He has played 47, and the stand-off points to a sale in January.
Villa originally paid Sunderland £18m for the player and an additional £3m after they secured Premier League survival, when Bent chalked up 25 appearances in a claret and blue shirt.
A Villa spokesman denied he is being left out for financial reasons.
Bent's former team-mate at Ipswich and Charlton, Matt Holland, said: "Sunderland may be due another chunk of money on him reaching 50 appearances, so it may be difficult to play him."