Mack stayed away from the first day of the three-day minicamp on Tuesday. He is subject to a fine of about $80,000 if he doesn't show up at all this week.
Mack is entering the final season of his rookie contract that is set to pay him $13.8 million. Mack is seeking a long-term deal and hasn't participated in the entire offseason program in the first year under new coach Jon Gruden.
"One of the big reasons I came here was to coach that man," Gruden said. "I don't want to speculate. There are a lot of guys in the league, several players in a similar situation. We're just trying to resolve it as soon as possible and in the meantime coach the players that are here."
Mack has been one of the top defensive players in football since being drafted in the first round in 2014. He was a first-team All-Pro at both defensive end and linebacker in 2015 and won AP Defensive Player of the Year in 2016. He has 40 1/2 sacks in four seasons and leads the NFL in QB pressures with 185.5 since entering the league, according to SportRadar.
"You can't replace Khalil," safety Karl Joseph said. "You know what he's doing. We respect it. I think the other guys have done a good job stepping up and learning the system like everybody else has been. When he's ready to come back, we'll be ready for him. You can't replace a guy like that."
The Raiders also signed free agent defensive tackles Ahtyba Rubin and Frostee Rucker on Tuesday and waived quarterback Christian Hackenberg and linebacker Brady Shelton to make room on the roster.
Rubin spent his first seven seasons with Cleveland before stints with Seattle, Denver and Atlanta the past three years. Rubin has appeared in 144 games and made 107 starts, while recording 428 tackles, 15 sacks, two interceptions, seven passes defensed, six forced fumbles and one fumble recovery.
Rucker spent the first six years of his career with Cincinnati before going to Cleveland in 2012. He spent the past five seasons with Arizona. Rucker has appeared in 142 games with 73 starts, recording 350 tackles, 21.5 sacks, one interception, 12 passes defensed, eight forced fumbles and three fumble recoveries.