Twenty three-time Grand Slam champion Serena Williams' ex-coach Rennae Stubbs said Novak Djokovic's serve was "pretty s**t" initially. "He would double-fault, his elbow was too low, there were a lot of things going on," added Stubbs. "You look at Novak's serve now...I would certainly not teach anyone Novak's service motion. I don't think it is great," she stated.