The unstoppable Williams sisters have come to a halt at this year's Wimbledon.

The duo was forced to retire from the Wimbledon women's match due to a viral illness taken on by sister Serena. Could this mean the end of the end for the two tennis superstars?

According to the New York Times, "She [Serena] had trouble several times performing basic tasks of hand-eye coordination, including picking up balls or catching ones tossed to her."

The Williams sisters have dominated the tennis circuit for more than a decade. It seems as though it would take more than a little bug to force them out of the game. However, it is likely that this could be the final step of their career.

"Venus and Serena are at the end of their careers," said U.S. Fed Cup captain Mary Joe Fernandez according to Fox Sports. "One is 30, one is 29. Hopefully, they're going to play for a little bit longer. But this is the next generation. I mean, this is who's going to be playing the next five, 10 years."

In the sports world, where a peak can be as early as preteens and middle age is ancient, the Williams sisters are way more on the former than the latter. How long can they keep up their performances?

The sisters do not seem to be letting go quite yet though, as both released statements ensuring their return to the competition next year.

Serena released a statement saying, "I am heartbroken I'm not able to continue in the tournament," it began. "I thought I could rally this morning, because I really wanted to compete, but this bug just got the best of me. I want to thank my sister, Kristina, Stefanie, and our teams for their support. We were all looking forward to a great match."