"I'm a big fan of his, and he is probably the greatest tennis ambassador we have ever had," Becker told BBC Radio Five Live.
"Having said that, he is not playing as well any more. Why? With age, more injuries come in, you recover much slower after long matches.
"But on the other hand, once he is on he is a genius and he has won 17 Grand Slams, so there is no reason why he shouldn't have another remarkable week or two."
The 32-year-old has been drawn in the same group as Djokovic for the Finals.