While Denver has made Emmanuel Mudiay available, according to Stein's sources, Boston is hoping to get a first-round pick for the 23-year-old guard.
Smart is out of action with hand lacerations and has at least another week before he returns to the court.
Despite his recent injury, Smart has proved to be an impact player for the Celtics while averaging 10.1 points, 4.7 assists and 1.3 steals per game this year.
He is especially valuable on the defensive end, which is why he remains a key part of the rotation (averaging 30.3 minutes per game, mostly off the bench) despite inconsistent offensive efforts.
The Celtics have made him available in trades, per ESPN.com's Adrian Wojnarowski. He will be a restricted free agent in the offseason, and the team already has a similar player in Terry Rozier.
The Nuggets could use Smart to help them reach the 2018 postseason. They are 28-25 this campaign, good for eighth in the Western Conference, and Smart would be a valuable addition to a defense that ranks 20th in points allowed per 100 possessions (109.2), per Basketball Reference.