McLeish is keen to sign him on a permanent basis - as long as he delivers.
The Villa boss said: "It all boils down to what he can give us on the field.
"We know the potential is there, we know the history of the guy and how well he can play. If he comes in and transforms the team then of course we're going to be interested.
"His best years are still in front of him and he should be coming to his peak. The motivation for him will be to show people what he is really capable of.
"Jermaine has got great incentives there to play a few more years and not look back on his career on think 'where has that gone?'"