James Harden is confident he will have improved mobility for Game 7 of the Brooklyn Nets' Eastern Conference semi-final series after appearing limited in the 104-89 loss to the Milwaukee Bucks.

Harden returned from a hamstring injury sustained in the series opener, playing both Game 5 and Game 6, but his mobility has visibly been restricted by the issue.

At one stage in Thursday's Game 6 defeat to the Bucks, former NBA MVP Harden swooped on a loose ball, offering up a fast-break opportunity but he instead held up play to ensure he did not need to sprint.

The Bucks levelled the series at 3-3, with forcing a deciding Game 7 at Barclays Center in Brooklyn on Saturday.

Harden's return coincided with Kyrie Irving's absence after he injured his ankle in Game 4, triggering further doubts about his fitness but the former insisted he was improving.

"It's not even about rust. It's about being able to move," Harden said after finishing with 16 points, five rebounds and seven assists from 40 minutes on court.

"Day by day I continue to get better. Game 5 was the first time I did any movement since I got hurt. Tonight was no different.

"I'm out there to do whatever it takes to win. I've got to be better on both ends of the floor which I will be on Game 7."

Nets team-mate Kevin Durant, who scored 32 points and had 11 rebounds for second-seeded Brooklyn, felt Harden seemed to be on the improve.

"He was moving better today. That's a tough, tough injury," Durant said post-game.

"He's gutting it out for us. We're not expecting too much from him movement wise. He's going out there and giving it his all. You've got to respect that."

Durant was not happy with the way his side defended Khris Middleton, who had a game-high 38 points and 10 rebounds.

"I think we fouled him three times shooting threes, which got his rhythm going," Durant said.

"He's a shot maker. We gave him confidence. Every time it felt like they got an offensive rebound he hit a three. He made timely shots for them."