The pair played together in Switzerland with FC Basle.
Sio told RMC: "Will Salah win the Ballon d'Or? I am not able to answer that question. There was only one Ballon d'Or in Africa, it's George Weah. Is Mohamed Salah able to continue like this every year? I think it's up to him to ask.
"He is someone who is in the middle of today and who reminds me a little of Antoine Griezmann. It is by working that he can stay at this level.
"I wish him the very best to be a Ballon d'Or one day because he will show his full potential, but as I told you, this story of Ballon d'Or is very complicated."