"He played very well and got off to a brilliant start but tired in the second half because he hasn't played too many 90-minute games," O'Leary said after the game.
"We'll get more than that out of him and he will prove a valuable player for many years to come - he's a threat.
"His pace worries defenders and he's given us a great option. He will prove to be a very good player eventually.
And on the game overall, O'Leary said: "My only disappointment was that we should have won by a mile.