Al Horford didn't play against the Boston Celtics on Thursday due to a knee injury, but he was shown on the jumbotron and received cheers — although there were some boos as well.

Horford spent the previous three seasons with the Celtics before signing with the Philadelphia 76ers this past summer. He signed a four-year, $109 million contract with Philadelphia.

One of the best pure professionals in the league, Horford wants Celtics fans to remember how hard he worked every night:

“I hope they remembered how hard I worked and that I gave everything to this team,” Horford told Jared Weiss of The Athletic. “I wish we didn’t come up short, but I’ll always love my time in Boston.”

Horford averaged 13.6 points, 6.7 rebounds and 4.2 assists last season with Boston while shooting 53.5 percent from the field, 36.0 percent from beyond the arc and 82.1 percent from the free-throw line.

The Celtics underachieved as a team last season and were dysfunctional. Horford, one of the leaders in Boston, knew that big changes needed to be made if the Celtics wanted to run it back and compete for a championship.

While changes were made in Boston with the departures of Kyrie Irving, Terry Rozier and Marcus Morris and the arrival of Kemba Walker, Horford just felt like playing with the Sixers gave him the best opportunity to win a championship. It also helped that Philly was willing to pay him a contract he was looking for.