Carter has been diagnosed with mononucleosis and is without a timetable for a return, Gary Washburn of The Boston Globe reports.
Carter missed Boston's final three preseason games with the illness and is now expected to miss time to begin the regular season. He can be considered week-to-week until Boston provides an update on his progress. The 2024 first-rounder signed a two-way pact with the Celtics on Saturday and will provide backcourt depth for the club.