Roger Federer's hopes of starting the American hard-court swing as world number one have been boosted after defending champion Jo-Wilfried Tsonga withdrew from the upcoming Rotterdam Open through injury.

The 20-time grand slam champion has to reach the semi-finals next week [12 February-18 February] to replace Rafael Nadal at the top of the ATP standings. Should he do so he will eclipse Andre Agassi as the oldest man at the summit of the men's game.

Federer is scheduled to face a qualifier in round one, with Philipp Kohlschreiber and Stan Wawrinka then standing between him and that historic last four berth.

Should the 36-year-old progress beyond the semi-finals then he will add further daylight between himself and Nadal, who does not play again until the Mexican Open in Acapulco [26 February-4 March].

Victory for Federer in his first appearance in Rotterdam will be enough to ensure he remains as world number one until the start of the North American hard-court swing which begins at Indian Wells next month.

Nadal has 300 ranking points to defend in Mexico, having finished as runner-up in 2017, but even should he take the title it would not be good enough to reclaim top spot.

Therefore, Federer's route to the title has been eased after news that reigning champion Tsonga has pulled out with a suspected hamstring tear suffered during defeat to Lucas Pouille at the Open Sud de France in Montpellier.

The former Australian Open finalist trailed 6-1 5-5 when he called time on his semi-final against fellow-countryman Pouille, and later admitted he could be faced with a lengthy spell out of the sport.

"A big [tear], a little one, I don't know yet, I'm going to have to have more tests," said Tsonga, according to ESPN. "I've reached a moment in my career where I need to make some choices about when I play."

Tsonga, who beat David Goffin to win last year's Rotterdam crown, was due to face a qualifier in his first match. A lucky loser from the ongoing qualifying tournament will now benefit from the development.

Last week, Nick Kyrgios became the first confirmed player to pull out after the number five seed claimed injury would prevent him from competing. He withdrew from last year's event to play in the National Basketball Association [NBA] celebrity game.

Roger Federer and Rafael Nadal
Federer hopes to eclipse Nadal next week in Rotterdam. Getty Images