Andy Murray has waded into a row with Lacoste CEO Thierry Guibert after the sportswear chief accused Stefanos Tsitsipas of 'unfair behaviour' for withdrawing from the ATP Finals.

Tsitsipas pulled out after three games against Holger Rune in their Green Group match in Turin. 

The Greek player seemed to have a back problem and will be replaced in the tournament by Hubert Hurkacz.

Jannik Sinner inflicted a first defeat on Novak Djokovic since the Wimbledon final in July, and while congratulating Sinner for his three-set win, Guibert took a dig at Tsitsipas.

'Hats off to @janniksin for his win tonight. Despite the unfair behaviour of Tsitsipas, he showed to everyone why he is a future champ and an authentic guy', he wrote on X, formerly Twitter. 

Murray hit back, writing: 'Bizarre post from a CEO of a sports brand. Getting injured is part of sport and isn't 'unfair behaviour'.

It is unclear exactly what Guibert found unfair about Tsitsipas, the 2019 ATP Finals champion, pulling out of the competition with injury. 

He was 2-1 down against Rune when he decided to call it quits because of his back pain, walking off to jeers at Pala Alpitour.

Tsitsipas said: 'It kills me not to be able to finish this tournament. 

'I had a little bit of trouble with my movement. It's mainly affected when I move. It's difficult to compete in the match without having to move. This is tennis. This is not darts.

'The pain was very big. I've gone through pain during matches in the past, and I endured pain, but this was clearly too much to handle 

'I had to take the difficult decision to do what I did. I felt it at the second game of the match. I actually felt it in the warm-up with my serve. Warming up on my serve, I felt very irritated and lots of pain hitting me on my back..

'It's very unfortunate. I've had two editions here in Turin where I had to withdraw from the tournament. Never happened to me before that I had to withdraw. 

'It definitely hurts me a lot because this is the tournament that means the most to me, including the Grand Slams. I'm not able to compete the way I want to compete.'