Chiarelli said during a news conference the agent for Thomas had passed the word on this week.
"So, as of now, I am operating under the premise that there's a strong possibility that he'll be taking a year off and we'd have to go about our business without Tim Thomas," Chiarelli said.
Thomas has only one year left on his current contract.
Thomas, 38, had a 35-19-1 record and a 2.36 goals-against average during the regular season in 2011-12. The Bruins then lost to Washington in seven games during the opening round of the playoffs.
He led Boston to the Stanley Cup title at the end of the 2010-11 campaign, the franchise's first in 39 years, and won the Vezina Trophy for the second time.
In 378 career regular-season games, Thomas has a 196-121-45 record. He is 29-21 in the post-season.