James Harden's hamstring injury left Brooklyn Nets coach Steve Nash "heartbroken" for the star shooting guard, whose NBA playoffs participation is in doubt.

Harden missed 21 games of the regular season due to a right hamstring problem and seemed to suffer a reoccurrence of the injury just 43 seconds into Saturday's 115-107 Game 1 win over the Milwaukee Bucks.

The Nets must now wait on the result of scans to determine the extent of the issue, though Nash was not overly positive.

"You know we got a lot thrown at us this year, so we were, in a sense, well trained for this event," Nash told reporters after the game.

"But you never want to see that for someone like James, who is such an important player and such an incredible player and cares so much.

"I'm heartbroken for him. I don't know what's going to happen. I don't know if he's playing the next game, if he's out. I have no idea. But I'm heartbroken for him that he had to miss tonight."

The Nets face the Bucks again on Monday, and Kyrie Irving knows how much harder their task will be without Harden.

"I mean, it's never easy to lose anybody, especially this time of the year where we just wanna have fun playing basketball and playing the right way and competing at a high level," said Irving, who scored 25 points and tallied a further eight assists.

"We're obviously out there for bigger reasons, so when you see the game snatched away so early from one of our brothers, we feel for him, and we just had to make a quick adjustment and just adjust from there.

"That's the best thing we can do. We just came in the huddle, made sure that everybody on the bench knew kind of the situation we were in, and like I said, we just played out from there. It went our way tonight, but obviously, we're gonna feel his loss no matter what."

Harden, 31, has averaged 24.6 points, 10.9 assists and 8.5 rebounds in his first season with the Nets since arriving from the Houston Rockets.