Derbyshire is back in England after leaving Rovers for Olympiacos last year, he is on a season long loan with Birmingham and Sam wonders why he has come back.
"I don't know why he is back, he told me that the place he wanted to be is Greece," Allardyce said.
"He said he didn't want to stay in this country, it's that good there he wanted to be there, so I don't quite know what has happened along the line. Obviously it's not quite as good as he thought it was.
"But he is a very good goalscorer, we all know that, and that is why we got an unbelievably good fee. We let him go there on loan and he became a hero, they paid a lot of money for him and we capitalised on that because we needed to. Over four million euros was one of the best deals, for him and for us that I've done in my time.
"Now he comes back, hopefully not to haunt us on Saturday, because we know that, particularly off the bench, he is good at turning a game with goals."