Heskey had only a bit-part role to play during the second half of last season following the arrival of club-record signing Darren Bent in January.
But McLeish said: "Emile's experience is phenomenal. He has enormous experience. He has played for England, he has played for several top managers over the years so he has learnt a lot."
He added: "Discarding his kind of knowledge and his skills would be crazy. I have to tap into a guy like that. I have to use him to the full.
"There is no guarantee that Emile will play every week - but he has certainly impressed me."
Heskey regained his spot initially after Gerard Houllier's arrival as manager last season but Bent's £18million capture saw him revert to being a back-up player.
Source: PA
Source: PA