BOSTON — Al Horford was looking so much forward to his first return to Boston since signing in the offseason as a free agent with the 76ers, but first trip back to TD Garden ended in frustration.

That’s because the Sixers forward-center was unable to play in Thursday’s 115-109 win at Boston due to left knee soreness and left hamstring tightness.

His status wasn’t determined until after Horford warmed up before Thursday’s game with the Boston Celtics at TD Garden.

“When I went on the floor, I just wasn’t ready to go,” Horford said in a pre-game interview with the media.

Horford, who signed a four-year free agent deal for $97 million that can grow to as much as $109 million with incentives, didn’t want his first trip returning to Boston to be as a spectator

“I played here, but always during the years, coming to play in the Garden is a big deal and a special place to play,” he said. “I am definitely disappointed that I won’t be able to play tonight.”

Actually so were the Boston fans.

Before the second quarter, Horford was shown on the jumbotron and the fans started loudly cheering, eventually giving him a standing ovation.

Horford acknowledged the cheers and waived to the crowd in appreciation.

According to Horford, he suffered his injury late in Tuesday’s 97-92 win over the visiting Denver Nuggets.

“It happened right at the end of the Denver game,” Horford said. “I didn’t think it was anything serious, but as the night went on it got progressively worse.”

So for the past two days he said he has received constant treatment and then hit the court Thursday morning for the Sixers shootaround.

“At the shootaround it wasn’t where I wanted it to be, but we still wanted to kind of keep it going,” Horford said. “I am just not ready; I won’t miss too much time.”

Horford is a five-time all-star, four with the Atlanta Hawks and one in three seasons in Boston.

Before the game, Celtics coach Brad Stevens cited Horford’s consistent excellence.

“Al is a really good person, a really good player and we won a lot of games with being a huge contributor on the court,” Stevens said. “You look at his stats and they are almost identical, the percentage, the points, the rebounds. He comes with the same thing every game and that says a lot about him.”

Stevens has a point about similar stats. During his three seasons with Boston, Horford averaged 13.5 points, 7.0 rebounds, 4.6 assists, 0.7 steals and 1.2 blocks.

This year in 23 games for the Sixers, Horford is averaging 13.8 points, 6.8 rebounds, 3.9 assists, 1.1 steals, and 1.0 block.

Why such consistency?

“He’s a pro,” Stevens said. “He is a normal guy in a lot of ways, comes to work and works hard and has won every place he has been,”

Horford is in his 13th season and has seen his team reach the playoffs each of the previous 12 years.

"He gave us an unbelievable bump when he came here and you can see it in Philly,” Stevens said.

This was the third game that Horford has missed. The other two came when the Sixers rested him on the front end of back-to-back games.