He said: "I'm pleased to see David come on and take his opportunity. It's up to him now. In the next few weeks he'll get some games and we'll see what he can do. It's been difficult for him. Benjani has done fantastic. He's not been able to get in the team because the other lads have played so well.
"But now he's going to get an opportunity to play. I would be a liar if I said he had shown he can perform in the Premier League. If he had he'd have been playing. I think he needs to adjust and it's been hard.
"But if he comes in and goes on a little run now, works hard and shows he can score goals, then he can get the opportunity to play.
"It's always a gamble when you take players from the Championship into the Premier. You hope they hit the ground running but David's not had a lot of chance to be fair.
"He's been unfortunate, especially once we've been playing this system with one up. I want him to do well, I bought him, nobody wants him to do well more than I do.
"Only time will tell. Hopefully he will prove a success - it's up to him."