Pierce did not make the flight to Orlando for a Christmas Day game against the Magic, one day after Kevin Garnett missed his first game of the season with a thigh bruise. Instead, team doctor Brian McKeon drained fluid from Pierce's knee at New England Baptist Hospital.
The Celtics are on a six-day, four-game road trip that will also take them to the Clippers, Golden State Warriors and Phoenix Suns before returning home for a Jan. 2 game against Toronto.
Pierce could be back for the Jan. 6 game at Miami.
The 2008 NBA finals MVP had played in every game this season, leading the team with an average of 18.2 points.
Celtics spokesman Jeff Twiss said Pierce complained of soreness in the knee after Tuesday night's game, when he missed his first 10 shots against the Indiana Pacers but wound up scoring 21 points. Garnett missed that game, the first he's missed this season.
The Celtics won their 17th NBA title in 2008 -- their first season with Pierce, Garnett and Ray Allen. But last year Garnett missed the end of the season and the playoffs with strained knee ligaments, and the Celtics were eliminated by the Magic in the conference semifinals.
With Garnett back in the lineup, Boston sped to the best record in the Eastern Conference, 22-5, just one game behind the defending NBA champion Los Angeles Lakers for the best record in the league.