Djokovic will play Bosnian Damir Dzumhur in the third round. But in the last few days, I've started to feel the abdominal a little bit - especially when I was serving. "I prefer not to play".
The win improved the Croat's prospects of making the ATP Finals in London starting on November 11.
Second seeded Djokovic has secured the world No. 1 spot following Spanish tennis great Rafael Nadal's retirement on Wednesday due to abdominal problems.
Djokovic, who seems to have reinvented the hunger, has managed to maintain the new-found consistency with titles at US Open and Shanghai Masters. So yeah, I'll give it a go tomorrow. "But the race is still there", added Djokovic. If I can do well here in Paris and beat (Djokovic), all the better, " Federer said.
Federer is coming in hot after winning his 99th career title, in Basel last week.
The four-time Paris champion faces Marin Cilic in the last eight on Friday.
When asked about the London finals he added: "I am very sorry but I can not answer you".
After some speculation about whether or not Roger Federer would actually compete in Paris, he confirmed his participation on Tuesday.
Elsewhere, German fourth seed Alexander Zverev, playing his 70th match of the season, defeated Frances Tiafoe of the United States 6-4, 6-4 while defending champion Jack Sock put out Richard Gasquet 6-3, 6-3.
World number 57 Herbert was beaten by Kazakhstan's Mikail Kukushkin in three sets (3-6, 6-3, 7-5) while Jeremy Chardy, ranked 40th, lost 6-4, 6-4 to Spain's Fernando Verdasco.
The fifth seed bounced back from a bruising defeat to Anett Kontaveit on Wednesday, but overcame Mertens 6-2, 7-6 in a tense round-robin tie in Zhuhai, southern China.