Anthony Slater of The Athletic noted that trainers had been working on Russell's thumb, which had bothered the guard for a "few minutes." He eventually went to the locker room in the third quarter and did not come back.
Russell had 12 points, seven assists and nine turnovers in 25 minutes before exiting. He had posted 25.7 points on a career-high 45.2 percent shooting, 6.7 assists and 3.8 rebounds per game in his first season for the Warriors entering Friday.
The left-handed guard has been sidelined in the past.
An ankle injury forced him off the court for three games earlier this season. Arthroscopic left knee surgery sidelined him for 32 contests during the 2017-18 campaign for the Brooklyn Nets, and knee and calf ailments played a part in him missing 19 matchups in 2016-17 for the Los Angeles Lakers.
Russell, whom the Lakers took second overall out of Ohio State in the 2015 draft, broke out during a 2018-19 All-Star campaign in which he averaged a career-high 21.1 points, 7.0 assists and 3.9 rebounds for a 42-40 Nets team that improved by 14 wins from the previous year.
The 23-year-old entered the 2019 offseason as a restricted free agent, but the Nets executed a sign-and-trade with the Warriors to bring Kevin Durant into the mix and send Russell to the Bay Area.
Russell has been productive for the Warriors. He was also shooting a career-high 37 percent from three-point range before the Celtics game.
However, Golden State has fallen under the weight of Durant's departure coupled with injuries to Klay Thompson (torn ACL) and Stephen Curry (broken left hand), going a league-worst 2-10 over their first 12 games.
Russell is a steady source of 25-plus points per night for an offense that needs help minus the Splash Brothers. The Warriors could use him back as soon as possible.
If he's forced to miss time, point guard Ky Bowman should see more minutes.
The rookie out of Boston College replaced Russell in the lineup Friday and during his three-game absence earlier this year. He is averaging 6.5 points and 2.1 assists in 18.3 minutes per game and posted 14.3 points and 5.3 assists while spelling Russell in the starting lineup.