Mike Budenholzer was unsure if Giannis Antetokounmpo would be fit for Game 5 against the Miami Heat, but the Milwaukee Bucks head coach's heart stopped when the star hurt his ankle.

Antetokounmpo left Sunday's 118-115 overtime victory in the second quarter after re-injuring his ankle in the NBA playoffs.

The reigning MVP had posted 19 points in less than 12 minutes before Khris Middleton inspired the Bucks with 36 points as they stayed alive in the Eastern Conference semi-finals.

But there is no guarantee Antetokounmpo will be back for Game 5 on Tuesday, with the Heat still leading 3-1 at Walt Disney World Resort.

"As far as for Game 5, they're evaluating him now," Bucks Budenholzer told a news conference.

"He'll get treatment through the night and we'll just see how he does over the next 24-48 hours and no, there was no consideration about him coming back today."

While it was Middleton who ended up keeping the top-seeded Bucks alive, Antetokounmpo was in fine form before his injury.

Budenholzer praised Antetokounmpo and said the injury was a scary moment for the Bucks.

"You feel for Giannis. I hope it's not lost what he did in those first 10 or 12 minutes on an ankle that is not fully 100 per cent," he said.

"He was phenomenal to start the game and gave us a huge boost. I think they threw a big punch early and Giannis was able to keep us afloat and when he went down, all our hearts just stopped for a second."

Heat star Jimmy Butler, who finished with 17 points, felt Miami fell away after Antetokounmpo's injury.

"We relaxed a little bit. We stopped playing basketball the right way. We stopped guarding. We stopped living by our defensive principles," he said.

"We weren't getting 50-50 balls, we were getting outrebounded, it was just all bad."