By Brian Robb, CBS Boston

BOSTON (CBS) — Could Rajon Rondo be a lifetime Celtic? Danny Ainge admitted a bit of revealing information yesterday on Toucher and Rich, making it public that the team had approached Rondo about signing a contract extension. After making Rondo the Celtics’ 15th captain in team history last week, it should come as no surprise that Ainge wants to lock up the team’s biggest asset on and off the floor for the foreseeable future.

The biggest question now is what price Ainge is willing to pay to keep his star point guard. The Celtics’ president of basketball operations was tight-lipped regarding that part of the equation during the phone interview.

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“We did talk to Rondo about extending him,” Ainge admitted. “But that’s all part of the negotiation that will happen again this summer and most likely the summer after. I don’t know [if Rondo will sign an extension], time will tell. In the collective bargaining agreement, there are limits on what can and can’t be done. Really it’s not that Rondo doesn’t want to accept an extension, as much as it’s just not financially smart for him to accept it right now. We didn’t think he would [sign], but we did try.”

So why exactly was Rondo unwilling to sign a deal an extension right now?

“I never want to discuss negotiations in the media, I think we’ve said enough,” Ainge said after furthering questioning from Toucher and Rich.

Due to the NBA’s CBA rules, it’s pretty easy to see how these negotiations likely went down. The rules are very restrictive on extensions, so Rondo agreeing to any kind of deal now would in effect be costing the point guard an opportunity at a much bigger contract in the coming seasons.

At the moment, Rondo is currently in the fourth year of a five-year $55 million dollar contract. He’s eligible to sign an extension at any point before becoming a free agent next summer, but the CBA places strict limits on what Ainge can offer Rondo in a deal.

According to Larry Coon’s CBA FAQ, extensions for veterans are limited for four seasons, including the years currently on the player’s contract. Therefore, since Rondo is already under contract for this season and next season, Ainge could only offer him two additional years to tack on to the end of his current deal. With Rondo likely seeking at least a four- or five-year deal in free agency, signing for an extra two right now wouldn’t make much sense for the point guard.

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Additionally, there’s the issue of money.  Right now, the Celtics have Rondo signed to a bargain deal compared to the rest of the NBA landscape; he’s making just under $12 million this season, far less than other top point guards on the market.

This dollar figure works against the Celtics in contract negotiations, since they are only able to offer Rondo up to 107.5 percent of his previous salary for the first year of the extension, which amounts to roughly $13.9 million dollars.

That’s a healthy offer from the Celtics, but isn’t nearly convincing enough for Rondo to accept the deal without exploring what he could receive on the open market. If he hits free agency, Rondo is eligible for a starting salary that would be above $16 million. Ainge acknowledged yesterday that Boston’s limited offer starting at $13.9 million for the extension wouldn’t be enough to satisfy Rondo for now.

“I think that Rondo will demand quite a bit in the open market. The competition for Rondo in free agency will be very high,” Ainge said.

As Ainge said, the negotiations for a Rondo extension won’t stop now. Once this season ends, the team will be able to add on an additional year to their offer, a contract that would run through the 2017-18 season. That would provide Rondo with some additional security and guaranteed money, something that might be appealing to a player coming off a torn right ACL.

The money still might not be enough for Rondo though at that point. Time will likely tell, based on his performance. For now though, the waiting game between the two sides continues, with the future of Boston’s captain remaining up in the air.

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Brian Robb covers the Celtics for CBS Boston and contributes to, among other media outlets. You can follow him on Twitter @CelticsHub.