Cahill says the England midfielder has not been affected by the uncertainty surrounding his future.
Cahill said: "The type of guy he is and the professional he is, and I think you can see from his performances, that it is not really affecting him. It will be great if Frank is around but, at the minute, we have just got this season to concentrate on.
"I don't think it is affecting him one bit and that is the most important thing for us moving forward. It is a decision for the club, it is not something us players can get involved in.
"He is a phenomenal player and he is in great form for us at the moment. He works hard on his game and it is no shock that has consistently scored over ten goals a season for the last ten seasons. I hope that continues."