The striker is on-loan from Borussia Monchengladbach.
Pardew said: "We know at this club that we need strikers and I'm hoping he can tick a box for us between now and the end of the season.
"To get him back to where he was is a process and that's the process he's going through. Our fans need to give him a bit of time and understanding because there is definitely a pedigree there.
"But, at the end of this period he will have had three-and-a-half months with us and he needs to be pretty close to his best if we are going to sign him."
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