Roger Federer does not want his pursuit of 100 ATP trophies to drive him crazy.

The tennis veteran has 99 titles to his name and is two victories away from his century of silverware.

He's trying to not overthink the milestone, which he says should be an enjoyable experience rather than an unpleasant, pressure-filled situation.

Federer plays Alexander Zverev in the ATP Tour World Finals semifinal on Saturday.

Victory would see him progress to Sunday's final against Novak Djokovic or Marin Čilić.

Roger Federer is on the cusp of a remarkable achievement in sport, but the veteran tennis player is doing his best not to think about it.

The 37-year-old has forced his way into a 2018 ATP Tour World Finals semifinal against Alexander Zverev on Saturday, and is just two victories away from clinching his 100th trophy.

Federer has been rooted on 99 titles since his success at the Swiss Indoors last month, when he beat Marius Copil in straight sets in Basel.

He attempted to win an unprecedented 100th trophy in the next European indoor tournament, but ended up losing to Novak Djokovic in the semifinal of the Paris Masters — one of the best tennis matches you'll see all year.

Federer is in another semifinal this weekend, but he's trying not to obsess over victory.

"I'm still not thinking of the number, 100," he said, according to the official ATP website.

The reason Federer does not want to overthink the milestone is because he does not want to create a pressure-filled situation for himself.

"I won't let that get in my head, make me go crazy because it should be something I'm excited about and not something I should feel extra pressure."

Federer lost his first group stage game in the ATP World Tour Finals when Kei Nishikori took advantage of Federer's many errors to claim a straight sets win on November 11.

Two days later, Federer bounced back to dominate Dominic Thiem, and then cruised to victory over Kevin Anderson on Thursday.

If he beats Zverev tomorrow it sets up a tournament finale against Novak Djokovic or Marin Čilić, who contest the other competition's other semifinal on Friday.

Federer, though, is unfazed at the prospect of back-to-back matches on Saturday and Sunday. He said: "I'm very happy that I still have energy left in the tank. Mentally, I feel fresh."