DENVER -- It was clear immediately something was wrong as Warriors forward David Lee grunted and grabbed the top of his right thigh.

"Ahhhh, I felt a pop," Lee could be heard saying on the video of the injury.

He was knocked out of his first career playoff game early in the fourth quarter of the Warriors' 97-95 Game 1 loss to the Denver Nuggets on Saturday. The preliminary diagnosis is a strained hip flexor.

The injury happened at the 11:34 mark of the fourth quarter. He drove down the right side of the key for a layup and was fouled in midair by Nuggets center JaVale McGee, knocking Lee off balance.

He came down on his right foot, which appeared to jam into the hardwood and cause an awkward contortion.

X-rays taken Saturday night were negative. Lee is scheduled to have an MRI on Sunday to determine the severity of his injury.

"It is unfortunate," coach Mark Jackson said. "He is certainly a highlighted guy for us, somebody we count on."

According to WebMD, the hip flexors are a group of muscles -- connecting the spine, the pelvis and the thigh bone -- that move the hip forward when running and walking. A hip flexor strain is the stretching or tearing of one of those muscles, causing pain when the knee is raised.

There are three levels of hip flexor strains: Grade 1 (stretching), Grade 2 (partial tear) and Grade 3 (complete tear). The MRI will tell Warriors' doctors if the hip flexor strain diagnosis is correct and which grade Lee sustained.

Lee had 10 points on 4-of-14 shooting with 14 rebounds and four turnovers in 29 minutes of action.