Alex Zverev Taken Off Court In Wheelchair After Bad Injury, Retires From Nadal Match

The epic French Open match between Rafael Nadal and Alexander Zverev came to an unfortunate halt on Friday ... after the German star was forced to retire due to a gruesome ankle injury.

The semifinal showdown had all the makings of being a classic -- Rafa won the first set in a tiebreaker ... and as Rafa positioned himself to force another tiebreaker, Sascha's ankle rolled and he fell to the clay.

Zverev screamed and writhed in pain ... as Nadal came to his side in support.

As it turns out, NBA star Kevin Love was in the stands at Roland Garros ... documenting the heartbreaking scene on his Instagram.

The 25-year-old was taken off in a wheelchair ... and eventually came back out on the court on crutches to officially retire from the match. The crowd cheered as he waved to the fans.

Nadal praised Zverev in a post-match interview ... and gave the #3-ranked pro a hug.