Wimbledon 2015: Serena Williams practises on Jack Nicklaus court

Serena Williams' French Open success this year was her 20th Grand Slam victory

Serena Williams says she is unfazed by the challenge of winning all four Grand Slams in a year, with her Wimbledon training including a hit on the grass courts of golf great Jack Nicklaus.

American Williams, 33, has already won the 2015 Australian and French Opens, with Wimbledon and the US Open to come.

"Personally it doesn't make it feel any different," said the SW19 top seed.

The world number one added: "Me and Venus were at Jack Nicklaus' place - it was fun. Very good courts."

Nicklaus, 75, is regarded as one of the best golfers of all time, having won 18 majors, including six Masters titles.

Jack Nicklaus, pictured with Roger Federer, has attended numerous Wimbledon tournaments

The American lives in North Palm Beach, Florida and handed over one of his three grass-courts to Williams and sister Venus to get in tune for Wimbledon, which begins on Monday.

Williams would become the first woman since Steffi Graff in 1988 to win all four Grand Slam tournaments in a calendar year, if she goes on to claim the Wimbledon and US Open titles.

But she is cautious ahead of her opening match against Russian Margarita Gasparyan, after suffering a fourth round exit in 2013 and going out in the second round last year.

"I don't feel any pressure to win all four," said Williams, who is bidding for a sixth championship at the All England Club.

"I really don't feel that pressure. Maybe if I would happen to win here, then maybe I might start feeling it after that.

"But for me being mentally tough is probably my biggest strength.

"Being the youngest of five children really made me have to scrap and be tougher.

"It's great to have a big serve, too. Ultimately you could be the best player in the world, but you still get down and you have to be able to come back."