Sources: Horford to be unrestricted free agent

Bontemps: Horford likely to return to Celtics (0:49)

Tim Bontemps expects Al Horford will return to the Celtics despite declining his option with the team. (0:49)

All-Star center Al Horford of the Boston Celtics will decline to exercise his $30.1 million option for the 2019-20 season and become an unrestricted free agent, league sources tell ESPN.

While Horford, a five-time All-Star, will move into the free-agent marketplace on June 30, there's motivation for both Horford and the Celtics to work toward an agreement on a new long-term contract, league sources tell ESPN.

Horford could help Boston's salary-cap flexibility with a new deal that starts below that $30.1 million salary.

Horford, 33, is a key member of the Celtics core and a favorite of management, coaches and teammates. Horford averaged 13.6 points and 6.7 rebounds for the Celtics this past season, his third with Boston since leaving Atlanta for a four-year, $113 million free-agent deal with the Celtics.

Horford has been to the Eastern Conference playoffs 11 times in his 12-year pro career. He won two national championships at the University of Florida.