Boston didn't make firm promises on playing time with Monroe, league sources said. His ability to score inside gives Boston another dimension as it prepares to make a push for a deep run into the Eastern Conference playoffs.
While the Pelicans could offer only Monroe $2.2 million for the balance of the season, the chance at a starting job -- in his childhood hometown -- still made for a compelling case with Monroe. But he ultimately chose the Celtics' ability to offer him more money based upon carving $5 million out of its $8.4 million disabled player exception awarded with the season-ending injury to Gordon Hayward.
Monroe agreed to a contract buyout on the remainder of his $17.8 million salary this season and will become an unrestricted free agent once he clears waivers on Saturday.
Monroe, 27, has averaged 11.3 points and eight rebounds in 23 minutes a game with the Suns. Before Monroe was traded to Phoenix, he averaged a career-low 6.8 points and five rebounds in limited minutes for the Milwaukee Bucks this season.
In Boston, Monroe might be best used in a reserve role. Coach Brad Stevens has leaned heavily on Aron Baynes in a starting spot given the toughness he adds alongside Al Horford. Boston's defensive rating is a team-best 95.5 when Baynes is on the court, and his offensive limitations are offset when running him alongside starters like Kyrie Irving. Boston's defensive rating spikes to a team-worst 102.2 when Baynes sits.
The Celtics have desperately needed an offensive threat when Irving goes to the bench, and Monroe could see plenty of touches with reserve units. His biggest competition for minutes will come from Daniel Theis, an offseason import from Germany who has slowly emerged as a key rotation player. For January, Theis averaged 6.3 points and 5.1 rebounds over 16.4 minutes per game. He also shot 47.6 percent beyond the 3-point arc in January and gives maximum effort on both ends.
Stevens said he couldn't comment on the possible signing of Monroe, but Marcus Morris called the veteran a "great piece" for Boston.
"I think that's a great pickup for us," Morris said. "Veteran player, knows how to play the game. He's been around the league a while so I think he'll add to our size down low, scoring ability. I think it's a great pickup.
"He's a big body. Even if he's not scoring, he's carving space for other guys to be able to drive. He's well-respected around the league so that goes a long way. I think he's going to be a great piece for us going forward."
Stevens will have to figure out where Monroe fits on a team that likes to spread the floor, and Monroe must commit to playing defense to win his coach's trust. Still, his offensive talents might be too tantalizing. Given all the maddening lulls that Boston's second unit has endured this season, Stevens can have reserve units feed Monroe when the offensive is struggling. Monroe gives Boston a much-needed post threat, and his passing talents will create open looks for teammates.
Monroe also becomes Boston's best rebounder from the moment he puts a jersey on. He can help a Boston team that ranks 14th in the league in total rebound percentage (50.2).
ESPN's Chris Forsberg contributed to this report.