Certainly it’s more serious that it appeared Monday night when Pierce pronounced it a “mild foot sprain.”

Pierce had an X-ray today and further tests were needed. According to Danny Ainge, the X-ray didn’t provide all the answers, and an MRI was scheduled.

Concerns ranged from a broken bone to ligament damage, said a source.

“Everyone hopes it’s not something that’s going to be a problem long term,” said one source, “but it doesn’t look good.”

Pierce suffered the injury in the first quarter Monday in Washington, leaving the game with 2:01 left. He returned with 7:53 to go in the second period and played the rest of the half.

Just before the break, he collided again with Butler. They knocked knees, and both players needed a while before they could get up and off the floor.

Doc Rivers said later he regretted leaving Pierce in the game.

“I shouldn’t have even played him in the second half, in my opinion,” he said. “I think I messed that one up. He wasn’t playing bad; I just don’t think he was moving well enough. And why take a chance? That’s the way I looked at it. It’s nothing bad, but I just sat him.”

The injury didn’t seem like a big deal later. Pierce had some ice wrapped on the foot, but when he removed it he was able to walk around the dressing room without any alteration in his stride

Pierce was moving in and out of the trainer’s room only because that’s where former Celtic Sam Cassell had set up shop with Kevin Garnett and others. Pierce was laughing loudly and showing no indications of discomfort.

He appeared to be fine, as well, as he got off the plane when the team returned home.