Gael Monfils has withdrawn from the ATP World Tour Finals ahead of his final round-robin match against Novak Djokovic with a rib injury.

World number six Monfils was moving gingerly during his 6-3 1-6 6-4 defeat to Dominic Thiem at the O2 Arena on Tuesday, his second loss of the competition after being beaten in his opener by Milos Raonic.

The Frenchman has not recovered from a rib muscle injury he initially sustained in Stockholm in October in time to take on Djokovic on Thursday, with David Goffin instead taking on the Serbian.

"I still feel worse and worse on my ribs," Monfils said at a news conference on Wednesday. "Unfortunately today I wasn't feeling great so I won't play tomorrow.

"I'm very happy and honoured to be here in the top eight. It's the greatest season I've ever had.

"I have a lot of hope for next year. With the new season I will have new challenges and hopefully be even stronger.

"You work so hard to be here. I'm disappointed but it will give me more strength next year."