The Belgian, 21, signed for the Blues in a £32million deal from Lille with a reputation for dazzling displays full of skill and invention.
As well as that he bamboozled Wigan’s defence with a mesmeric performance before being replaced by fellow summer signing Oscar.
And Di Matteo admitted that watching him in full flow is a delightful experience: “He looks a real threat. It was a real pleasure to watch him.
“We are very happy to have him in our team.”
Meanwhile Di Matteo remained coy on the club’s possible plans to add another player to their ranks before the transfer window ends.
But the Blues boss has insisted bringing in new players isn’t essential as they already have strength and depth in their team.
He added: “I’m quite happy with the squad and with the team that we have. There is some real quality and competition. So we’ll see.”