World no 2 Carlos Alcaraz withdrew from the ATP 500 tournament in Acapulco with a right hamstring strain while Cameron Norrie pulled out due to fatigue, the tournament organisers said.
"Unfortunately I won't be able to play in @AbiertoTelcel. I have a grade 1 strain in my right hamstring that will keep me out for several days, according to the tests we did this morning," Alcaraz tweeted.
"I'm really sad I can't compete here, but now it's time to think about recovering and being ready as soon as possible. I hope to see you all soon!" he added.
Alcaraz owns an 8-1 record on the season after winning the Argentina Open and reaching the final of the Rio Open. The Spaniard missed more than three months following last year's Paris Masters due to injury.
Norrie claimed the biggest clay-court title of his career in Brazil, where he battled past Alcaraz in the final. The left-handed Briton leads the ATP Tour in match wins this season with 18 (18-3).
"Unfortunately I have to withdraw from Acapulco," Norrie said in an Instagram Story. "It's one of my favourite tournaments, so it's really tough for me to withdraw." "We wish you both a speedy recovery," the Acapulco tournament wrote on social media.