The 21-year-old also had his left lower leg strapped in his first-up win over Feliciano Lopez on Sunday, but said at the time it was due to a recent injury sustained playing basketball.
"Just relax. Jesus Christ. Far out," he said. "I just had a little bit of a knee pain the last couple of days, it has actually been troubling me for the past couple of weeks." "Obviously the first match back a couple of weeks ago was tough and I am just getting used to it again, but hopefully it gets warm soon and it will ease off."
Copyright Agence France-Presse, 2017