He told Sky Sports: "Put him in an Arsenal team, put him in a Liverpool or a Man United team, he scores 30 Premier League goals in a season. I think anyone who disagrees with that hasn't been watching the last two-and-a-half years.
"I think there are five clubs in the world who could probably end up buying him and he will improve any of those clubs by a mile. He turns Manchester United into challengers for the Premier League.
"Having scouted players not just for their technical ability but their personality and their growth for 18 years, I think he's not even in his prime even though he's turning 28.
"Whoever buys him, 100m will be well spent because he's coming into his prime. You're going to get five or six years of his best.
"He's scored a goal every other game in the Premier League for Brentford. Put Ivan in an Aston Villa team under (Unai) Emery and see how many goals he scores in the Premier League. He'd probably be up there for the Golden Boot."