The 19-year-old joined the Baggies on loan in August 2012 and has since racked up 22 first-team appearances for the Midlands club, hitting the back of the net nine times in the process.
Dembele is adamant that the teenager "has everything" as his Spurs side prepare to take him on at the Hawthorns on Sunday.
"I know Lukaku quite well," the former Fulham man told the Sunday Mirror. "I'm not surprised he is doing so well at West Brom.
"It's not so easy to go to a club like Chelsea as a young guy but everybody in Belgium knows what he's capable of.
|11/1||Romelu Lukaku is 11/1 with Bet365 to score the first goal in a West Brom win over Spurs
"It’s not for me to decide what Chelsea need but I know Lukaku is a very good player and I'm happy he plays for my national team.
"I don't doubt he has the quality to play for Chelsea. He is a very good player and I'm sure he will succeed there."
Tottenham failed to strengthen significantly during the transfer window other than the arrival of Lewis Holtby from Schalke, about whomo Dembele admits that he knew little.
"I am very happy we signed Lewis Holtby," the Belgian enthused, "but, to be honest I don't know a lot about football. I don't watch too much football at home, I only watch the Premier League, so I knew Lewis by name but I didn’t know him very well as a player.
"A lot of people told me he's a very good player and I see this now as well but everybody was impressed with him in the first training session and when he came on against Norwich, everybody saw he is a very good player."