BOSTON – Rajon Rondo is quickly becoming one of the top point guards in the NBA, so the Celtics have a tough choice to make on whether or not to extend his contract before Monday night’s deadline.

If they don’t, then Rondo will become a restricted free agent next summer.

The Celtics initially offered Rondo a five-year deal worth a reported $45 million, but Rondo and his agent Bill Duffy believe he should be paid as one of the top five point guards in the league and they demanded a five-year reportedly worth between $55 million and $60 million.

The Celtics don’t want to pay him that much if they don’t have to. But by not giving in to his demands, they could end up paying him a lot more if he is offered more than that in free agency next summer and if they want to keep him.

Celtics president of basketball operations Danny Ainge, on his weekly scheduled appearance on WEEI, explained the process that the Celtics are going through for evaluating whether or not to extend Rondo’s contract before time runs out on Monday.

“It’s a difficult situation because is he risking a bigger contract for next year [if he decides to sign]? Are we risking paying him more than having to match a contract next year? Ultimately he wants to be here,” Ainge said. “We want him here so it’s kind of trying to figure out the future and what’s sort of money is out there. There is a lot of money out there in the free agent market next year. There are a lot of teams with cap space.

“There are a lot of teams that like Rondo as I found out this year with all of the draft rumors…Potentially he could make more money than he’s even asking. Potentially he could make less. It’s all about finances and trying to predict the future.”

Ainge said it has been hard to predict just how much Rondo will improve over the next five years and to determine his monetary value. There is no question that Rondo (6.7 points, 12.3 assists, 5.7 rebounds, 2.3 steals) has gotten better every year since being drafted by the Phoenix Suns 21st overall in 2006 and then traded to the Celtics. He proved in the playoffs last season that he can put a team on his back and carry it like he did in the playoffs last season when he nearly averaged a triple-double (16.9 points, 9.8 assists, 9.7 rebounds).

Ainge said that Rondo is not a max contract player right now, but he could be in a year or two and the Celtics need to consider that during this process.

“You go through all of the statistics. You weigh where he’s at this stage in his career versus Steve Nash or Tony Parker, all of these other guys, Chauncey Billups, where they were in that phase of their career. You try to do as many evaluations as you can,” Ainge said.

“He is a difficult guy to evaluate because he’s unique in his game. When we won the championship, there were games where it was tough to put him on the court and then there were games where he was the best player among four Hall of Famers on the court. He was the best player in the gym, better than Kobe [Bryant]. Better than Paul [Pierce]. He was the best player out there so he is unique and it’s difficult…We’re hoping that he just continues to progress and he’s our guy for a long time.”

Ainge said that it is not “critical” for the Celtics to extend Rondo’s contract by Monday’s deadline because of the fact that they can match any offer he gets after the season. But if they want to keep him, they could end up paying him a lot more than they want to if it comes to that.

There are a lot of teams that will have a lot of money after this season because they are saving up for a deep free agent class that includes All-Stars LeBron James (Early Termination Option), Dwyane Wade (player option), Dirk Nowitzki (ETO), Chris Bosh (player option), Ray Allen and Amare Stoudemire (ETO) among others.

As teams miss out on whoever they are initially going after, they will take their money to the next budding star, and Rondo will move up on that list. For example, Ainge said, this past summer, restricted free agents Marcin Gortat (5 years, $34 million), from Orlando, and Utah’s Paul Millsap ($32 million for 4 years) received a lot more money from other teams than what their incumbent teams wanted to pay them. In the end, their initial team ended up paying a lot more money for them than they wanted to.

That could happen with the Celtics and Rondo.

While some of Rondo’s success can be attributed to him playing with three future Hall of Famers in Pierce, Kevin Garnett and Ray Allen, Ainge said that Rondo can be successful without them.

“He’s proven statistically in his young career, these last three years, that he plays every bit as effective with one of the stars on the court as he does with all three on the court,” Ainge said. “Last year in the playoffs, there was no KG and he’s out there and he averages almost a triple-double in the playoffs and Paul was struggling through some of the games...He had two of those guys out there but he didn’t have all three of them so the notion that he needs all three of those guys for him to be effective is [bogus].

“The bottom line is he’s young, he’s durable, he’s got great characteristics and he’s a guy that we would like to have around. This [Nov. 2] deadline doesn’t really have any bearing on whether we have him around for the future or not.”

Boston coach Doc Rivers said that he believes that Rondo will be a Celtic for his entire career.

roblee@projo.com