The Raiders released Bruce Irvin, their sacks leader and highest-paid defensive player this season, on Saturday.

“We would like to thank Bruce Irvin for his years of service to the Oakland Raiders and we wish him the best,” general manager Reggie McKenzie said in a statement.

Irvin posted a brief note on Twitter thanking Raiders owner Mark Davis, McKenzie, head coach Jon Gruden and the Raiders for his time with the organization.

“I will always cherish my experience with the Oakland Raiders,” Irvin wrote. “As the seasons change, so do our roles and I look forward to continuing my journey with the NFL!”

Irvin, 31, was named a team co-captain to start the season but saw his role shrink dramatically in recent weeks. Irvin played just nine defensive snaps in the Raiders’ 34-3 loss to the 49ers on Thursday night.

Last season, Khalil Mack and Irvin formed one of the NFL’s more productive pass-rushing duos, combining for 18.5 sacks. After Mack was traded to the Bears on Sept. 1, Irvin, in a new role as an edge-rushing defensive end, was expected to head up the Raiders’ pass rush.

Irvin had three sacks in eight games for a Raiders defense that ranks last in the NFL with seven sacks, and he totaled just six tackles while playing 48 percent of the team’s defensive snaps.

On Friday, head coach Jon Gruden said Irvin’s nine snaps against the 49ers reflected his playing only in certain personnel groupings.

“We’re a 4-3 team, we’re not a 3-4,” Gruden said. “In the base defense, sometimes he doesn’t fit the role that we need done. No disrespect to Bruce, but he’s an edge rusher. We haven’t had a lead. We haven’t had the opposition behind the chains a lot. So his role has been reduced. And I know he’s frustrated. I’m frustrated. And we’ll try to solve that as soon as possible. He’s a good player.”

One of six co-captains named before the season, Irvin is the second to depart following Derrick Johnson, who was released Oct. 16. His exit also follows that of veteran cornerback Dominique Rodgers-Cromartie, who announced his retirement last week.

Having already traded Mack and receiver Amari Cooper in deals that netted three first-round draft picks over the next two years, the Raiders were reportedly shopping Irvin before the Oct. 30 trade deadline but did not execute a deal.

Irvin is guaranteed his base salary of $8 million this season, the remainder of which the Raiders will owe him unless Irvin, a vested veteran, is claimed off waivers by another team. If not claimed, Irvin would become a free agent. The Raiders do clear $9.25 million in salary cap space next season that would have gone to Irvin, according to overthecap.com.

According to spotrac.com, by trading Mack and Cooper and parting with Irvin, the Raiders have cleared about $45 million in salary cap space in 2019.

Irvin signed a four-year deal with the Raiders in 2016 after playing his first four seasons with the Seahawks. In 40 regular-season games with Oakland, Irvin had 18 sacks and 11 forced fumbles.

Moved from outside linebacker to a primarily pass-rushing role this season — a move that he said felt “more natural” — Irvin had a goal of double-digit sacks for the first time in his career. But he was on the field for fewer than half the defensive snaps in four of eight games, including a total of 33 snaps in the last two games.

Two of three rookie defensive linemen the Raiders selected in April, Maurice Hurst and Arden Key, had played more snaps this season than Irvin. With Irvin gone, Hurst is the lone Raiders player with multiple sacks — two.

Matt Kawahara is a San Francisco Chronicle staff writer. Email: mkawahara@sfchronicle.com Twitter: @matthewkawahara