The Boston Celtics saw their roster change drastically during free agency with Kyrie Irving and Al Horford leaving to sign elsewhere.

According to ESPN's Brian Windhorst, the Celtics have suggested that the Philadelphia 76ers tampered with Horford prior to free agency getting underway last month. 

"The Celtics were, from what I am told, one of the teams that kind of stomped their feet about what they felt was tampering," Windhorst said. "Not with Kyrie, although that looked like it was lined up pretty far in advance. But with Horford. What happened with Horford – again, from what I am told – really upset the Celtics, that they were thinking they were going to be able to negotiate with him, talk to him about a new contract, and all of a sudden, it was like he already knew what his market was and was out of there."

Horford ended up signing a four-year, $109 million contract with the Sixers after spending the last three seasons with the Celtics. The deal was agreed upon shortly after free agency began in June, which leaves the Celtics to believe that there was tampering.

As Windhorst alluded to, the Celtics believed that they would have an opportunity to negotiate with Horford once free agency opened.

On the other hand, Boston agreed to a four-year, $141 million contract with former Charlotte Hornets guard Kemba Walker right after free agency began. It certainly could be assumed that the Celtics had a similar agreement in place with Walker that the Sixers may have had with Horford.

During his final season in Boston, Horford put together averages of 13.6 points, 6.7 rebounds, and 4.2 assists while shooting 36.0 percent from beyond the arc. Horford will join a Philadelphia core of Joel Embiid, Ben Simmons, Tobias Harris, and Josh Richardson as the team re-signed Harris and acquired Richardson in the Jimmy Butler trade earlier this offseason.