Madison Keys, who lost to Simona Halep in the fourth round of Wimbledon, admitted that she was very tired and anxious during the match, which may have caused her to cramp up.

“I think it's probably a combination of exhaustion, just playing a lot of matches and being kind of tired,” Keys said. “But nerves, as well. I think that played a part in it. So I think it was probably just a bad combination.”

The ninth-ranked Keys, who reached the semifinals of the 2015 Australian Open, broke into the Top 10 last month after winning the title in Birmingham. But she says she still has work to do.

“I'm not totally satisfied with what I have achieved,” Keys said. “I think I can do more. I want to do more. So even being young, it's great. But at the same time, I want more.”