Roger Federer's quest to regain the world number one ranking in tennis has been boosted by news that Nick Kyrgios has withdrawn from the Rotterdam Open due to injury.

After winning his 20<sup>th grand slam title at the Australian Open in January, Federer, 36, is now out to reclaim his place at the summit of men's tennis for the first time more than five years after taking a wild card into next week's competition in Netherlands.

The Swiss trails current number one Rafael Nadal by 155 ATP points but with the Spaniard currently recovering from a hip injury that ended his Australian Open campaign at the quarter-final stage, he can clinch top spot again for the first time since October 2012 simply by reaching the semi-finals in Rotterdam.

That route is by no means a given with Stan Wawrinka, Grigor Dimitrov, Alexander Zverev and defending champion Jo-Wilfried Tsonga competing next week but the withdrawal of Kyrgios, the fifth highest-ranked player in Rotterdam next week, could make things easier.

The 22-year-old withdrew from Australia's Davis Cup match against Germany last week, explaining on Twitter on Friday morning [9 February] that an elbow injury means he is unable to compete.

"I was really looking forward to finally making my debut in Rotterdam in front of the great Dutch crowd that I have heard so much about but unfortunately injured my elbow during the Davis Cup in Brisbane," Kyrgios wrote on Twitter.

"I have tried to do all I can to be ready to play and have left the withdrawal as late as possible but unfortunately I ran out of time and won't be able to play. I wish Richard [Krajicek, tournament director] and the organising team the very best for another great event and I hope top finally be in Rotterdam in 2019."

Kyrgios and Federer could have met in the quarter-final stages in Rotterdam.

If the Swiss can reclaim top spot, he will extend his record for most weeks at the top of the rankings, which currently stands at 302, while he will also replace Andre Agassi as the world's oldest world No.1, a record the American held when he was 33.