World ranking: 4
Champion (2002 & 2003)
Serena arrives at Wimbledon with the Australian Open title under her belt but in uncertain form after a string of injuries in 2005.
The 23-year-old has struggled with shoulder and ankle problems and even battled through a rib injury to beat Lindsay Davenport to the Australian crown.
Injury then forced her to retire at Amelia Island and saw her tumble to defeat against Francesca Schiavone at May's Rome Masters.
And the American also withdrew from the French Open because of a persistent ankle problem.
While Serena's long-term committment to the game may be in doubt, the American always delivers at Wimbledon.
She has her best Grand Slam record on grass, winning the title twice and finishing as runner-up to Maria Sharapova last year.
A spell away from the draining competitive circuit will see her return with renewed vigour - which should be enough of a warning for Serena's title rivals.