'Serve vital to Maria Sharapova French Open success'

Tennis coach Nick Bollettieri says Maria Sharapova's serve must be firing on all cylinders if she is to complete a career Grand Slam by winning the French Open.

Bollettieri, Sharapova's former coach, says Sharapova - who required surgery on a shoulder injury in 2008 - says the Russian will need to have confidence in her serve, especially as a healthy Serena Williams, whom he describes as the best player in the history of the women's game, will prove a "difficult foe".