Khalil Mack Oakland Raiders
Bruce Irvin #51 and Khalil Mack #52 of the Oakland Raiders celebrate after a play against the New York Giants during their NFL game at Oakland-Alameda County Coliseum on Dec. 3, 2017 in Oakland, California. Lachlan Cunningham/Getty Images

Two of the Oakland Raiders’ best players won’t suit up when the team plays its first preseason game of the year Friday night. Both left tackle Donald Penn and Khalil Mack have made consecutive Pro Bowls, but it’s unknown when or if either player will wear the silver and black again in 2018 because of contract issues.

Mack will likely play for Oakland at some point this season, though he hasn’t reported to training camp as he seeks a new deal. Penn is almost fully recovered from a foot injury he suffered in December, and the organization reportedly wants him to take a pay cut when he returns.

Penn held out for most of training camp last year, eventually reporting in late August and getting a new two-year contract after Week 1. The team wants to rework the final year of the veteran’s deal, as first reported by the Las Vegas Review-Journal, and a refusal to do so could possibly spell the end of his time in the Bay Area.

NFL Media’s Ian Rapoport suggested that the Raiders could release or try to trade Penn if he doesn’t agree to take a little less than the $9 million—$3 million of which is guaranteed—he’s set to make this season. First-round pick Kolton Miller has impressed this summer, giving Oakland another option at left tackle if they decide to move on from Penn.

The Raiders don’t have that kind of backup plan when it comes to Mack. Oakland’s defense needs the help of one of the league’s top pass rushers after the unit finished 23rd in yards allowed last season.

It’s hard to believe that Oakland would trade Mack a year before he’s set to hit free agency and become eligible for the franchise tag, though it’s not inconceivable. An NFC team executive told Bleacher Report’s Mike Freeman that the odds of Mack being dealt are “increasing every day.”

“There's a feeling the Raiders are open for business when it comes to Mack,” the executive told Freeman.

Mack had a team-high 10.5 sacks in 2017 after winning the 2016 Defensive Player of the Year award. He had a career-high 15 sacks in 2015 when he started his string of three consecutive Pro Bowl appearances.

Mack has never missed a game in his four-year career. Penn had played in every single game since 2007 before Lisfranc surgery forced him to sit out Week 16 and Week 17 last season.

Oakland went 6-10 last year and missed the playoffs, cutting their win total from the previous season in half. Five AFC teams have better Super Bowl odds than the Raiders.