"If you are human, you should feel very sorry for a colleague," Nadal said.

"To see a colleague like this, even if for me it's a dream to be in the final, is not the way that we want it to be."

Zverev said it "looked like a very serious injury" in a video message posted on Instagram on Friday night.

"The medical team and doctors are still checking on it. We will let you know as soon as we know more," he said.

"It is not an easy moment for me."

Third seed Zverev screamed in pain when he went down on the baseline after turning his right ankle on the final point of the 12th game of the second set.

A concerned Nadal went round to check on his opponent as a medic raced on to the court to help the 25-year-old German.

The seriousness of the situation was immediately clear, with Zverev screaming and signalling for help as he lay on the clay.

Medics quickly arrived and it seemed obvious he would not be able to continue once the wheelchair was called for.

Afterwards, Nadal said it was "not easy" to talk following the incident.

"The only thing that I can say is I hope he's not too bad," added 36-year-old Nadal, who will play Norwegian eighth seed Casper Ruud in Sunday's final.

"Hopefully, it's just the normal thing when you turn your ankle and hopefully nothing is broken."