Horford, 34, plans to remain with his Oklahoma City teammates and train at the team facility, but he won't play in the final 28 games for the Thunder.
"We've talked with Al from the time he became a member of the Thunder this offseason about the many ways in which he would be able to help us as we entered the early stages of the necessary transition of our team," Thunder general manager Sam Presti said in a statement Saturday. "From day one Al has been a consummate professional and has had a tremendous influence on the team on and off the floor with his work ethic and total commitment to his teammates.
"Our conversations have been open and ongoing about how to maximize this season for him personally as well as the development of our team. Al has been nothing short of spectacular and will remain a part of the team as we build on an approach and mentality that we have taken for some time."
Since arriving from Philadelphia in a draft-night trade, Horford has been considered a significant presence and influence on the Thunder's young, rebuilding roster, and the organization was eager for Horford to remain among them as the two sides worked through this decision.
"When I arrived, I understood the direction of the team, we had a great individual plan in place for me, and I feel like as a result I've played really good basketball for the Thunder. At the same time, I know what it's like to be a young, aspiring player, and at this point in the season I understand how important playing meaningful minutes is for their careers and their development," Horford said in a statement. "I also understand how important it is for the organization to give them that opportunity.
"I'm looking forward to supporting the guys who supported me, watching them continue to play the right way and play together as we have throughout the season, while still being around the team and continuing my training."
After the season, Horford will have two years and $53 million left on his contract. Presti has pledged to work with Horford and his agent, Jason Glushon, on finding the center a trade to a team that fits better with this late stage of his career, sources told ESPN.
Sitting out protects Horford against injury that could complicate the ability to move him in the offseason. Horford has averaged 14.2 points, 6.7 rebounds and 3.4 assists this season. After joining the 76ers on a four-year, $109 million free-agent deal in 2019, Horford was traded to the Thunder on draft night in 2020.
The Thunder recently lost star guard Shai Gilgeous-Alexander for an extended period with plantar fasciitis. It was inevitable that Horford eventually would be shut down this season, but the loss of Gilgeous-Alexander expedited that timeline, sources said.
The Thunder could have three first-round picks in the 2021 NBA draft, based on a number of protection and pick-swap scenarios. The Thunder have been surprisingly competitive with such a young, unaccomplished roster, tied currently with the New Orleans Pelicans at 19-25.
Oklahoma City has 17 first-round and 17 second-round picks under control through the 2027 NBA draft.
This is Horford's 14th NBA season, including stops with Atlanta, Boston and Philadelphia. He has averaged 13.9 points, 8.2 rebounds and 3.3 assists for his career and twice has been an All-Defensive Team choice.