Warnock was part of England's World Cup squad last summer but was frozen out of the plans of McLeish's predecessor, Gerard Houllier.
The former Liverpool player trained with the youth team or reserves under Houllier and his Villa Park days looked numbered.
But McLeish insisted the slate was "wiped clean" for any player when he took charge last month and he has been impressed by the approach of Warnock.
McLeish said: "Stephen's attitude has been phenomenal and that's what I expect of top pros playing at a top level.
"He's trained really well. He played for England not so long ago and I think he's a terrific player.
"I need to see if he can be part of the future here.
"He has come back in and for me has staked his claim with his attitude alone."