Alexander Zverev has denied using his phone during his match against Stefanos Tsitsipas at the ATP Finals.

Zverev was asked about the incident at a news conference after he was seen touching something in his bag at a changeover during Wednesday's defeat.

The 22-year-old German, who lost 6-3 6-2 at London's O2 Arena, said: "I don't know what they saw, but it was definitely not a phone."

Rules state players cannot access any electronic devices during matches.

"My phone was in the locker room. I always leave it there," added Zverev.

Asked what he might have been touching, he said: "I mean, a water bottle? Empty water bottle maybe?"