The team extended a qualifying offer of $1.05 million to Stiemsma, ESPN reports, making him a restricted free agent, which allows the Celtics to match offers from other teams.
Stiemsma, 26, has been in the NBA just one year. He had 2.9 points, 3.2 rebounds and 1.5 blocks a game for the Celtics in 13.9 minutes of playing time last year, but he was also key in bringing energy and an extra inside presence to the court at times.
The 6-foot-11, 260-pound center also battled through foot injuries last season.
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