ALAMEDA — The Raiders’ offseason program began Monday without star defensive end Khalil Mack.

Mack was not present for the start of the voluntary session Monday morning when the Raiders met for the first time under coach Jon Gruden.

The news was first reported by NFL Media.

Mack is scheduled for one-year salary at $13.846 million under a fifth-year option invoked a year ago by the Raiders.

Mack, Gruden and general manager Reggie McKenzie are hoping for a long-term contract extension.

In terms of average salary, the NFL’s highest-paid defender in 2018 is Kansas City Chiefs defensive end Justin Houston, who is scheduled to make $20.6 million.

Mack is most often compared to Denver Broncos outside linebacker Von Miller, who is working under a six-year, $114 million contract with an average salary of more than $19 million and $70 million in guaranteed money.

Those two deals are probably the starting point for McKenzie in terms of getting a deal done with Mack.

Mack’s decision to forgo a voluntary session is an indication the two sides have a ways to go, although a contract of that size can take time.

Last season, the Raiders didn’t sign quarterback Derek Carr to a five-year, $125 million contract extension until June 22.

“I’m sure there will be some surprises,” Gruden said Sunday night on the eve of the first day. “It is voluntary, and obviously we’d love to see everybody here, because we are new and we’d like to start selling our system of football to them and making sure they can get in the best shape they can possibly be.”

McKenzie can be deliberate when it comes to contract negotiations. Left tackle Donald Penn sat out all of training camp a year ago because of frustrations over a negotiations to add more money to a deal which had begun in February.

The Raiders have more than $8 million in salary cap space, according to overthecap.com, although there are some contracts that aren’t yet accounted for. Mack’s $13.846 million is the second-highest cap figure on the roster behind Carr’s $25 million. That figure could actually be lowered with a long-term deal, assuming the first year gives Mack a minimum salary and prorates bonus money over the length of the contract.