BOSTON (CBS) — The Boston Celtics and Marcus Smart could not agree to a contract extension prior to Monday night’s deadline, and the guard will now become a restricted free agent next summer.

The Celtics want Smart to be part of their long-term plans and Smart would like to continue his career in Boston, but no deal makes Smart’s agent, Happy Walters, pretty un-happy.

READ MORE: Marty Walsh Tells CNN He Will Not Run For Governor Of Massachusetts

“But Wyc (Grousbeck) doesn’t want to pay the tax,” Walters told The Boston Herald on Monday night. “They’re into the tax already with three guys who make $30 million a year. If they want someone to take a discount, maybe it should be someone who has already made $150 million in their career, not someone who is just up and coming.”

Walters is referring to the max contracts the Celtics gave to Al Horford and Gordon Hayward over the last two summers, along with Kyrie Irving, who is making $18.9 million for this season. He questioned Boston’s window with those three, noting Horford’s age and Irving’s contract, which is up after the 2019-20 season.

“How long is that window going to last? Those guys have gone to Boston with the expectation they’re going to get better,” he said. “Al is getting older. They’ll have to figure out what they want to do with Kyrie again.”

Smart will be a key part to Boston’s success this season, both as their defensive specialist off the bench and with his improved jump shot — not to mention his new slimmer frame. With no deal on Monday, he’ll be motivated to go out and have a career year, earning him a massive payday over the summer. The Celtics will be able to match and deal Smart receives on the restricted free agent market.

Celtics president of basketball ops. Danny Ainge told 98.5 The Sports Hub’s Toucher & Rich on Tuesday that this is a no-lose situation for Boston.

READ MORE: Nearly Half Of COVID Hospitalizations In Massachusetts Are 'Incidental'

“Marcus is a big part of our team, as everyone in Boston knows. He helps us win games in so many different ways with a lot of intangibles. I also think he’s going to have his best year of his career coming up,” said Ainge. “I feel like it’s a no-lose situation for us. If Marcus blows up and has a breakout season, that’s great for us. We can match an offer, negotiate a deal before he goes out in restricted free agency. It allows us to maintain flexibility.

“Because we have three max contract players, these decisions are crucial. Every dollar we spend is important,” he added. “We have owners who will pay the luxury tax; they did it throughout the [Kevin Garnett] era. The luxury tax is not an issue we’re trying to avoid, but it’s very penalizing now, more so than then. We just have to be really careful as we build this team.”

Things could get tricky if a team decides to throw a monster deal his way, which is something Walters alluded to on Monday.

“It will cost them a lot more then, I can tell you that,” said Walters.

The Celtics, according to Walters, didn’t start negotiations with Smart until last Thursday.

MORE NEWS: Dunkin' Customer Accused Of Throwing Hot Coffee, Latest In String Of Mask Rage Incidents

“We’re being really reasonable,” he said. “Whatever we can work out, we’ll work out.”