"He was under contract," Gruden said of Mack. "He never showed up for an OTA, he never showed up for training camp, and it was obvious he wasn't going to show up for the season."
The defensive end held out the entire preseason seeking an extension beyond the final year of his rookie deal in 2018. He was eventually traded to the Chicago Bears, where he was able to quickly agree to a six-year, $141 million contract extension.
Mack also had kind words about the Raiders after the deal:
Gruden had also admitted that his team's offer wasn't comparable to what Mack eventually got from the Bears.
"We made an offer," the coach said last week, via Nick Shook of NFL.com. "I don't believe we were anywhere close to where the Bears were. The Bears made us an offer that we thought was really unique."
That offer entailed sending the Bears' next two first-round draft picks to the Raiders, along with a swap of other 2020 picks for balancing purposes.
Mack had already proved himself as an elite player with the Raiders, earning three Pro Bowl selections and one Defensive Player of the Year award in 2016. He was named first-team All-Pro in both 2015 and 2016 and has totaled 36.5 sacks over the last three years.
He was just as good in his first game with Chicago Monday against the Green Bay Packers, filling up the stat sheet with a sack, forced fumble, fumble recovery and an interception returned for a touchdown.
Regardless of what the Raiders eventually do with the draft picks acquired in the trade, Gruden will likely have to answer questions about Mack for a long time.