Billups said it's an "inflamed tendon" on the inside joint of the foot and that it's "not related" to the left Achilles' tendon injury that required surgery in February and sidelined him through the first 14 regular-season games.
Billups, 36, said he dealt with back, calf and foot problems while he was rehabilitating his Achilles' injury.
"I think this is just kind of part of the process," Billups said. "Frustrating, of course, working that hard to come back and then kind of sit back and wait. But I know what it is. I respect the process. I'm not like down at all. Of course I want to be out there, but it is what it is and I know it's all about the marathon for me."
Billups said the foot became painful Monday night during the Utah game. He couldn't push off the left foot, saying it was "really weak and I couldn't explode off of it."
He got an MRI exam on the foot Tuesday.
"It's something I've been dealing with even before I played my first game," said Billups, who has played in three games this season. "It was something I really wanted to get checked out because I just kind of felt I worked way too hard to get back and play hurt. ... It's inflamed a little so you just kind of give it time until it's ready, until it calms down."
Billups warned by NBA for a flop
When Clippers Coach Vinny Del Negro told Billups at the team's shoot-around Wednesday that the NBA had issued him a warning for a flop in the Utah game, Billups said his response, with a smile, was: "All right."
Billups kicked out his left foot while shooting a three-pointer late in the fourth quarter, getting fouled by Mo Williams on the play.
Billups made two of three free throws to tie the score.
"They call it a flop, I call it gamesmanship," Billups, a 15-year veteran, said. "I worked hard to get that. I learned that from some great players. I'm not going to let that go because of what they are trying to do. I'm going to play how I play."
If Billups gets warned again for flopping, he'll be fined $5,000 by the NBA.
Willie Green, who started again in place of Billups, also has issues with his right knee.
Del Negro said Green has some meniscus issues.
"He's been fighting through this all year," Del Negro said. "Willie is a warrior and he's going to give me everything he has."