BOSTON — Boston backup point guard Tony Allen limped into the Celtics locker room last night with his headphones on and his head down.

He was clearly upset that he would not get the opportunity to help Boston avenge its first loss of the season against Indiana.

Allen injured his right ankle in the second quarter Monday night in Boston’s victory over Orlando. He returned to the game later in the second quarter and finished with six points and two assists in 19 minutes, but he said that he shouldn’t have returned to the game, because playing worsened his ankle injury.

“It’s just sore,” Allen said. “Basically I just twisted it. I should have stayed off it against Orlando, but I tightened it up, went and got it taped, and I came back and I put more pressure on it than was already on it from the twist.”

“I didn’t want to go down like that,” Allen said of why he returned to the game on Monday. “I fought back but when I woke up the next morning I could barely walk. That’s why I said I should have just stayed off it.”

Allen said that one of his first thoughts when he twisted his ankle was the 2006-07 season, which ended prematurely for him (knee injury).

He hasn’t been the same since his knee injury, though he has shown flashes of his old self, like his 23-point outburst against Detroit on Nov. 9.

“When I got back to the locker room, the first thing I said was, ‘not again,’ ” Allen said. “I just prayed. They looked at the x-rays and they said it was nothing bad, just a sprained ankle. I am going to get an MRI just to make sure that everything is safe and go from there.”

Allen got treatment on his ankle last night and he is scheduled to get an MRI today.

Allen said that he hopes to return to Boston’s lineup tomorrow against Portland, but Boston coach Doc Rivers said that he doesn’t think Allen will be available until Sunday.

Allen said that he’s happy with his play so far this season, but he said that he still has a lot of work to do.

“Tony has been very, very good,” Rivers said. “I’m always on him but there are things offensively I want him to get better at — just being more consistent. The turnovers, he’s had a high turnover year so far. I’m always on him about his defense because I think he can be not just a good defender, a dominant defender and he hasn’t been that yet. He’s been good, very good, but I think with his strength and ability, and just his nature, he’s a tough, tough kid, that he could be just an unreal defender.”

With Allen out, Eddie House and Brian Scalabrine got to play more minutes last night.

Celts wanted Granger

Indiana star forward Danny Granger (24.7 points, 5.4 rebounds, 2.6 assists) was nearly a Celtic.

If Indiana did not take Granger with the 17th overall pick in the 2005 Draft, Rivers said that Boston would have taken him with the 18th pick.

“I was loving that he was falling to us,” Rivers said. “Honestly we were happy either way but Granger was the guy we wanted. We thought that he would have been just perfect for our team. We were looking at him and when it got to that pick we were either going to take Granger or Gerald Green.”

Indiana selected Granger so Boston took Green.

“Granger so far has turned out to be better but Gerald is a lot younger,” Rivers said. “There is still time for him but it would have been nice … I thought [Granger] had a chance to be a terrific player … and he is terrific. He’s going to be a star.”

Sympathy for Mitchell

Rivers and Indiana coach Jim O’Brien both feel bad for Sam Mitchell, who was fired by the Toronto Raptors (8-9) yesterday.

“I don’t know Sam very well but I hate to see any coach get fired,” said O’Brien, who had his first NBA head coaching job with the Celtics from 2001 through January 2004. “It’s a tough situation but I think he’ll land on his feet. He’s a quality coach,” O’Brien said of Mitchell.

Mitchell, 45, was replaced on an interim basis by assistant coach Jay Triano. Mitchell was the NBA’s coach of the year for the 2006-07 season, and had been Toronto’s head coach since 2004.

“That’s our job. When you win you get to stay a little bit and if you lose you just hope that Danny Ainge is on your side,” Rivers said.

roblee@projo.com