BOSTON — As practice wound down Friday for the Boston Celtics, Robert Williams was walking on a treadmill under the supervision of trainers.

Williams is working his way back from a concussion suffered Tuesday after taking an inadvertent elbow from Kevin Love. Coach Brad Stevens said Thursday that Williams wasn’t showing symptoms while starting his progression through the concussion protocol by riding a stationary bike. But Williams didn’t respond well.

“He didn’t feel great after (Thursday) so they dialed him back, so he’s back to day one again,” Stevens said. “We’ll see how he feels after today. That’s kind of the way that progression works. So he’s at the early stages of it.”

Players must pass a series of tests by completing a physical activity and not feeling symptoms. Once he passes all off the tests, he’ll be cleared to return.

Romeo Langford was back on the floor. The rookie wing slipped on a wet spot on the TD Garden floor Sunday and sprained his knee. Thursday he was seen on a stationary bike as practice wound down, but Friday was able to do a little more.

“Romeo actually did some of the non-contact portion of practice, moving pretty well,” Stevens said. “He looks pretty good. We hope for at least full practice by Monday.”

The Celtics plan to practice Saturday and take a day off before returning Monday to gear up for the opener Wednesday night at Philadelphia.

PISTONS: Detroit signed forward Tre’Shawn Thurman and waived guard Craig Sword.

The Pistons signed Sword on Thursday.

A DAY AFTER Commissioner Adam Silver said Chinese officials wanted Houston General Manager Daryl Morey fired, a spokesman for China’s foreign ministry said no such demand was made.