Campbell struck for Olympiacos in their shock Champions League win over Manchester United this week.
"I will decide that later. Why not? We bought him to bring him here," the manager said.
"He was good, convincing going forward [against Man United]. He looks like he has adapted a bit better to the physical side of the European game.
"We always knew that he had the talent to create something special. He did rely a bit too much on that.
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