He feels the Nigerian - who is due to start talks over a new deal - will have a major task to follow last year's dramatic form.
"Peter Odemwingie was one of the main reasons they've done so well," Di Matteo told the Birmingham Mail.
"We found him in Russia at Lokomotiv Moscow.
"It was one of those where you get a DVD, like the player, do some research and it worked out.
"It was credit to our scouting network. I think he has had a great season and obviously we saw all the goals he scored.
"It will be difficult to top that. He is a great player, he works very hard for the team, always in the top three of distance covered, works for everybody.
"I hope he can do it again because he's a great personality, great character and enthusiastic - but it will be tough for him."