Hold your breath, Suns fans ... Kevin Durant injured his ankle during pregame warm-ups on Wednesday night -- and now, there's fear the ailment could keep him out of the rest of the regular season.

The new Phoenix superstar was getting in some shots before what was supposed to be his first-ever home game as a Sun against the Thunder at Footprint Center ... when his left leg buckled.

You can see in video of the play, Durant's ankle folded on itself ... sending the 34-year-old crashing to the hardwood in pain.

The forward -- who was just traded from Brooklyn to Phoenix last month -- popped back up and continued warm-ups for a little bit ... but he ultimately went into the locker room for further evaluation, and didn't return.

KD ended up missing the game -- and he was seen leaving the arena in a walking boot. Later on Wednesday night, the Arizona Republic reported he now could miss the next four-to-six weeks.

The Suns went on to win without Durant ... and after the game, head coach Monty Williams said he didn't have a timetable for his injured star when he was asked about the injury.

"We'll probably get some more imaging just to make sure everybody's on the same page," Williams said.

Durant has hardly played for the Suns since the blockbuster trade -- he had been nursing a knee injury when he was dealt to Arizona, and has only logged time in three games with his new team since the swap with the Nets.

Playoffs begin in less than a month ... get better soon, KD.