World number three Carlos Alcaraz (21) is unlikely to be at his best for Wednesday’s ATP Finals match against Andrey Rublev (27) as the four-time Grand Slam champion continues to struggle with illness, the Spaniard’s coach Juan Carlos Ferrero said.

An off-colour Alcaraz lost 6-1, 7-5 to Norway’s Casper Ruud in his opening match on Monday and the Spaniard cancelled a public training session the following day.

“As soon as he moves a little, it’s hard for him to breathe. His chest is a bit tight. It’s a bad time to get sick,” Ferrero told reporters on Tuesday.

“We should not anticipate whether or not he will play tomorrow. We have all played in these circumstances. I don’t think he’s going to be so bad that he won’t be able to play. It’s going to be difficult for him to be 100% tomorrow.

“Rublev is a player who moves a lot, you have to be very good on your legs and, right now, that’s what’s costing him a little more, recovering between points.”

Alcaraz won the Beijing title in October but his form since winning Wimbledon earlier this year has been unconvincing, suffering a second-round exit at the US Open and being beaten by Ugo Humbert in the round of 16 at the Paris Masters.

After taking on Rublev later on Wednesday, he faces world number two Alexander Zverev in his final round-robin match of the eight-man event.

Alcaraz reached the semi-finals of the ATP Finals last year, where he was beaten by eventual winner Novak Djokovic.