John McEnroe believes Alexander Zverev is facing the most important moment of his career, with the tennis legend warning that this year's French Open could shape the German's legacy forever.
Zverev has moved into pole position to claim a maiden Grand Slam title after a dramatic series of exits transformed the men's draw at Roland Garros.
The world No 3 progressed to the semi-finals with a straight-sets victory over Rafael Jodar and now finds himself among the leading contenders for the title.
With Jannik Sinner and Novak Djokovic already eliminated and Carlos Alcaraz absent through injury, many believe the tournament has opened up perfectly for Zverev.
However, McEnroe has suggested the pressure on the German has never been greater.
The seven-time Grand Slam champion believes victory in Paris could be the breakthrough that unlocks further success, but warned failure may leave lasting questions hanging over his career.
"Everyone, including myself, feels he is going to win this," McEnroe said on TNT Sports.
"It could open the door for winning multiple ones.
John McEnroe believes Alexander Zverev is facing the most important moment of his career, with the tennis legend warning that this year's French Open could shape the German's legacy forever
|REUTERS
"Or it could be the other side of the coin: if he doesn't win this, he'll never win.
"So there's a lot riding on this for Sasha."
Despite being viewed as the favourite, Zverev still faces a significant obstacle in the form of rising Czech star Jakub Mensik.
The 20-year-old has enjoyed a remarkable tournament and arrives in the semi-finals full of confidence after defeating Brazilian teenager Joao Fonseca.
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French Open winners since 2000 | GETTY/GB NEWSMensik has rapidly emerged as one of the most exciting young talents in the sport and McEnroe expects him to remain a major force for years to come.
"I'll tell you, he's going to be a handful for the next 10 years," McEnroe said.
The American was particularly impressed by Mensik's athleticism and attacking style.
"Zverev, at 6ft 6in, moves side to side incredibly well," he added.
"But he's not quite as good moving forward as Mensik.
"He moves forward so well and he's a big guy."
McEnroe also highlighted the Czech's powerful serve as a major weapon capable of causing problems for any opponent.
"When you serve that big, it's by far the biggest shot in the game," he said.
Alexander Zverev is just two victories away from a maiden Grand Slam title | REUTERS"He's taking the ball on and being more aggressive."
The former world No 1 believes that could create additional pressure for Zverev despite his status as favourite.
"He will start stressing because he's still the heavy favourite," McEnroe said.
"But Mensik will cause some problems because if he keeps playing like he did, it will be interesting."
There are questions over Mensik's physical condition after he came through a demanding route to the last four, including two five-set matches.
The Czech also appeared to struggle physically during parts of his victory over Fonseca.
Yet McEnroe does not believe fatigue will be a decisive factor.
"Here's the good news for Mensik - he's not playing for a couple of days," he said. "And he's 20. It's amazing how quickly you bounce back at that age. To me, that's a non-issue. It's how he handles the pressure."