World No. 2 Carlos Alcaraz retired from his first-round match at the ATP Rio Open on Tuesday after rolling his right ankle on just the second point of the contest against Thiago Monteiro.

Despite taking a medical timeout and having the ankle taped, the Spanish star managed to win the first game. However, after dropping his serve in the second game, he called it quits, adding to what has been a disappointing 2024 campaign so far.

After the match, Alcaraz told reporters that withdrawing was a precaution. He also mentioned that the physiotherapists who treated him had indicated that the injury "is not serious."

"I spoke with the physiotherapist on the court, and we decided, together, that I would continue to see if it improved. It didn't, so we preferred to be careful and withdraw as a precaution," Alcaraz said, adding that he would have further tests on Wednesday.

The two-time Grand Slam winner's tough start to 2024 included a four-set defeat by Alexander Zverev in the Australian Open quarterfinals.

Last Saturday, he fell to 21st-ranked Chilean Nicolas Jarry in the semifinals in Buenos Aires and hasn't won an ATP title since his stunning Wimbledon triumph over Novak Djokovic last July.

Hopes that he could start turning things around in Rio – where he lifted the trophy in 2022 and finished runner-up to Britain's Cameron Norrie last year – were quickly dashed.

He and 117th-ranked Brazilian Monteiro were two points into the match when Alcaraz's right foot stuck in the red clay surface at Jockey Club Brasileiro, where rain had delayed the start of play for three hours.

Four of the day's tennis matches were postponed until Wednesday, and the first players to take the court on Tuesday played in misty conditions.

"That had cleared by the time Alcaraz and Monteiro squared off, and Alcaraz said court conditions were not to blame.

"Those things happen, even more so on clay," Alcaraz said.

"It wasn't a problem with the court; I got hurt in a change of direction, and that happens on this type of surface," added the Spaniard, who was slow to rise after taking a hard fall, limping to his chair, and putting a towel over his face before the trainer arrived.

Alcaraz's coach, Juan Carlos Ferrero, looked on with concern from the stands as Alcaraz, with a grimace and a slight limp, returned to action and won the opening game.

But after dropping his serve in the second, he opted not to continue.

"It's really sad to win in this way because I know how hard every player works to be ready for a tournament of this magnitude," Monteiro said.

"I just wish him a speedy recovery, that it's nothing serious, or that it won't affect his season," added the 29-year-old left-hander, who improved to 2-0 against Alcaraz, whom he beat in the round of 16 of the Melbourne-1 in 2021.

The injury comes with Italy's Australian Open champion Jannik Sinner closing in on Alcaraz's world No. 2 ranking.

Alcaraz leads Sinner, who won the Rotterdam title on Sunday, by just 535 points and has 1,000 points to defend next month at the prestigious hardcourt tournament in Indian Wells, California.