Most players have found the O2 Arena court very quick but Federer claimed it was slower than in previous years.
Federer suffered a shock straight-sets defeat to Kei Nishikori last night and blamed part of the loss on him needing to adjust to the court speed.
“I think it plays different or it’s definitely slower than I think the last three tournaments that I’ve played,” Federer said.
“So I think everybody’s making a minor adjustment, you know. So am I.”
Meanwhile, Zverev needed two tiebreaks to edge past Marin Cilic this afternoon and he was then quizzed on the state of the court.
And the German believes the high speed makes it difficult to find consistency.
“It is very fast,” Zverev said.
“It is definitely one of the quickest courts we have on tour.
“It is tough to find your rhythm on it.”
More to follow