The Rockets’ first option to fill the void left by Trevor Ariza’s departure also walked out the door Monday.

Forward Luc Mbah a Moute agreed to a one-year contract to return to the Los Angeles Clippers just days after Ariza officially signed his one-year, $15 million deal with Phoenix.

Unlike Ariza, who received a hefty contract offer in the first hours of free-agent negotiations, Mbah a Moute accepted the sort of contract, worth just $4.3 million, that the Rockets could have offered with a portion of their taxpayer mid-level exception.

Mbah a Moute’s departure, first reported by ESPN, will leave the Rockets scrambling to rebuild a defense that helped key their run to the NBA’s best record last season but will not be a cost-savings move once they complete their roster moves.

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The Rockets remain optimistic they can sign 10-time All-Star Carmelo Anthony when he becomes a free agent, two individuals with knowledge of the team’s thinking said. But with Mbah a Moute and Ariza gone from a team that improved to sixth in the league defensively, the Rockets likely will seek to sign a young prospect with strong potential on defensive.

The Rockets have shown interest in James Ennis, an athletic small forward who played for Rockets associate head coach Jeff Bzdelik at Memphis; Treveon Graham, a free agent who played sparingly at Charlotte last season; and James Nunnally, an outstanding shooter with defensive ability who played in Turkey.

A decision from Ennis’ camp is expected by Wednesday, a person with knowledge of the talks said. Depending on Ennis’ salary, the Rockets could spend more on Ennis in salary and taxes than they would have if Mbah a Moute had accepted their $2.4 million offer because Mbah a Moute’s years of service would have had his salary cost just $1.5 million and count that much in tax calculations.

Mbah a Moute, however, would have been a natural fit to replace Ariza. Mbah a Moute averaged 7.5 points, making 36.4 percent of his shots last season.

If Mbah a Moute can bounce back from the shoulder problems he had last season, his value to the Rockets was clear. It was made especially apparent in the postseason, when he was unable to come back from a dislocated shoulder — his second of the season that was suffered in the final week of the regular season. Mbah a Moute made just 25 percent of his shots in the postseason, falling out of the rotation entirely, and his absence was conspicuous in the Western Conference finals against Golden State.

The Rockets again will have to make up for losing him. They could have offered Mbah a Moute up to $5.3 million, their taxpayer mid-level exception, but could have sought to save that or much of it for Anthony. Mbah a Moute’s one-year deal with the Rockets, if they were not using their mid-level exception, would have been worth $2.4 million but would have given him early Laryy Bird rights next summer to exceed the salary cap to re-sign with the Rockets.

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With the luxury taxes the Rockets would have had to pay, assuming they sign center Clint Capela, Mbah a Moute’s contract would have cost the Rockets roughly $6 million in salary and taxes. The Clippers’ offer would have cost them roughly $16 million.

Instead, while still trying to get a deal with Capela, the Rockets will be trying to make up for summer losses with their “run it back” plan taking a second significant hit.

"On one hand, I'm happy for (Ariza) because it's a really good salary," Rockets coach Mike D'Antoni said. "I get it. On the other hand, we're going to miss him. He was the best professional player and friend that you could have as a coach.

"Luc did a great job for us. You don't win 65 games without everybody being good and a part of it.Now it's time to regroup and find a new crowd."

jonathan.feigen@chron.com

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