WALTHAM, Mass. – The blank banner hangs on the wall above the Boston Celtics’ practice court — a white rectangle with a green border.

If the current players want that filled in with the words “World Champions,” like 17 others adorning the gym, this season very well could be their last chance to accomplish that feat.

That’s what Coach Doc Rivers told aging stars Paul Pierce, Kevin Garnett and Ray Allen, and the rest of his players before their first practice of training camp Friday night.

“I was very honest with them about that,” Rivers said. “That doesn’t mean we don’t have some of them back next year or not, but there’s a chance we will not and this is most likely our last shot.”

Allen, who like Garnett is in the final year of his contract, has heard that before.

“I’ve heard that every year that I’ve been here,” he said. “I don’t look at it any different. I count each day. I feel like I’m on borrowed time right now.”

Rajon Rondo has plenty of time. Just 25, he’s the star point guard who gets The Big Three the ball. At least for now.

For the second straight year, the sometimes moody Rondo has been the subject of trade talks, even being mentioned in a possible deal for Chris Paul of the New Orleans Hornets. But after meeting with Rivers and the president of basketball operations, Danny Ainge, Rondo said he’s comfortable.

“They were straight up with me. They were honest,” Rondo said. “Teams were calling. I don’t think they were trying to intentionally ship me, but obviously you have to entertain the calls. So (Ainge), he told me he wanted me here and I’m still here, so far.

“I’m excited to be here. I’m familiar with this organization and I just want to get better and win a championship this year.”

To do that, the Celtics need a veteran bench. Ainge has assembled that after ending last season with just six players under contract.

On Friday Boston finalized a deal for guard Keyon Dooling, entering his 12th season, along with a protected second-round draft pick while sending the Milwaukee Bucks the draft rights to center-forward Albert Miralles. Rivers hoped forward Brandon Bass could practice with the Celtics soon. Bass’ agent, Tony Dutt, said a deal was being finalized that would send Bass to the Celtics for forward Glen Davis.

The Celtics also signed free agent forward-guard Marquis Daniels, who spent the early part of last season with them, free agent center-forward Chris Wilcox, starting his 10th season, and center Greg Stiemsma, who last played for Sioux Falls of the D-League.

Forward Jeff Green, a restricted free agent obtained from Oklahoma City last season, agreed to a one-year deal, Rivers said, but didn’t practice because the NBA had not approved the paperwork for the contract.

“We wanted players who were hungry and wanted to play with a sense of urgency,” Rivers said, “and I think Keyon fits that bill as well as anybody we could have gotten in the backup role.”

On Friday, though, Rivers had only nine players to work with, so assistant coach Tyronn Lue participated in practice as the 10th man.

“It’s a different first day of practice, I’ll say that,” Rivers said.

Allen, starting his 16th season, said it was “by far” his oddest opening day of camp in his career.

“You get so used to doing things a certain way and this is our livelihood. This is what we’ve been doing most of our lives,” he said. “When those leaves start to fall, you know pretty much where you are and for me, I was inside my house looking out the window telling my landscape guy, ‘Hey, you missed a batch of leaves over there.’

“I’m always micromanaging everything around the house so it’s good that I’ve got a day job now.”