Former Grand Slam doubles champion Mark Knowles admitted he was surprised by the fact that Novak Djokovic ran out of energy in the Belgrade final but believes the Serb will be where he needs to be when the times comes for the French Open. After suffering a 6-2 6-7 (4) 6-0 loss to Andrey Rublev in the Belgrade final, Djokovic indicated the illness he was battling was the likely reason for him collapsing in the third set versus Rublev. “Well I think I’m a little surprised,” Knowles said on Tennis Channel’s Inside-In podcast, as quoted on Sportskeeda,.”It’s come out that he …