Morgan did not suit up for Ontario's Thursday night matchup against the Iowa Wolves.
Morgan was placed on the injured list by the G League's Ontario Clippers on Saturday for an undisclosed reason.
The Clippers waived Morgan on Oct. 4, Law Murray of The Athletic reports.
Morgan was cut loose by the Pacers on Thursday, Adrian Wojnarowski of ESPN reports.
Morgan was traded from the Celtics to the Pacers on Friday along with four other players and a 2023 first-round pick in exchange for Malcolm Brogdon, Adrian Wojnarowski of ESPN reports.
Morgan (COVID-19 protocols) agreed Sunday with the Celtics on a multi-year contract, Shams Charania of The Athletic reports.
Morgan won't be available for Wednesday's game against the Bulls after he was placed in the NBA's COVID-19 health and safety protocols.
Morgan signed a 10-day contract with the Celtics on Monday, Adrian Wojnarowski of ESPN reports.
Morgan logged 20 points (7-8 FG, 4-5 3Pt, 2-5 FT), 11 rebounds, two assists, one steal and one block across 31 minutes during Sunday's 110-107 win over the Fort Wayne Mad Ants.
Morgan logged 18 points (7-11 FG, 1-4 3Pt, 3-4 FT), 10 rebounds, nine assists, one steal and one block across 31 minutes during Sunday's 145-141 win over the Delaware Blue Coats.