The Clippers and Mavericks continue to be linked to the 33-year-old forward, according to a report from the Boston Herald.
Horford initially declined his player option with the hopes of working out a new three-year deal with Boston, but now he wants to move on.
Horford declined his player option with the hopes of working out a new deal with the Celtics, but he now wants to sign with another team.
Horford is planning to leave the Celtics and sign a four-year contract with a different team, according to a report from the Boston Herald.
Al Horford and the Celtics want to work out a new deal in July.
Horford, 33, has one year remaining on a four-year, $113 million deal and a player option he may decline for the 2019-20 season.
Kevin Durant led the Golden State Warriors past the Houston Rockets, while the Boston Celtics won in Milwaukee on Sunday.
Giannis Antetokounmpo was made to work hard for his 22 points as the Milwaukee Bucks fell to defeat against the Boston Celtics.
“Our focus was to make sure that we made it tough on him every time," Horford said. "All of our guys, at different times, were on him."
A 110-106 win over the Indiana Pacers in Game 4 gave the Boston Celtics their first playoff sweep since 2011.