Carlos Alcaraz will have tests on the ankle injury that forced him to retire two games into his Rio Open first-round match.

The world number two required medical attention after twisting his ankle during only the second point of the match against Brazil's Thiago Monteiro.

The 20-year-old Spaniard returned to the court and managed to break his opponent's serve in the opening game.

But the two-time major winner retired after Monteiro immediately broke back.

"Tomorrow I'll have a test for my ankle and let's see if it's something serious or not," said Alcaraz, Rio champion in 2022 and runner-up at the tournament last year.

"I felt bad. That was the first impression I had. I was feeling pain once I fell down, so I thought it was going to be difficult to continue if I was still having those feelings.

"After a few points it didn't feel better. I couldn't move well and I knew that it was going to be impossible to continue.

"I thought it was going to get worse if I kept playing for such a long match and that's why I chose to retire."

Reigning Wimbledon champion Alcaraz is due to face compatriot and 23-time Grand Slam champion Rafael Nadal in The Netflix Slam on 3 March.

He will then hope to be fit enough to defend his Indian Wells title next month.