Hleb signed a loan deal from Barcelona on the last day of the transfer window, but missed Blues' match against Liverpool with an ankle injury picked up while playing for Belarus.
McLeish revealed that he has not yet decided what kind of role Hleb will have at The Hawthorns.
"He's looking quite good," he said.
"It was great to see him on the training field, he has undoubted quality.
"He's a little bit behind the other players in terms of games played. He had two international games that would have really sharpened him up but he came back with slight injuries.
"He's trained this week and looks good. I just have to make a decision as to whether I throw him right in or whether he comes on from the bench."
Chilean Jean Beausejour, who also signed for Blues on deadline day, is likely to be amongst McLeish's substitutes.
He lacks match fitness, having only just ironed out problems with his work permit.
McLeish said: "Again, I've seen him for the first time in a training session (on Thursday). He had problems with a visa coming back into the country.
"He did a session on Wednesday, which was the other players' day off.
"He looks strong, he looks quick, and I think he's a player that will excite the fans."