Mack responded to a tweet from Ted Nguyen of The Athletic by saying: "I miss it."
Raiders quarterback Derek Carr replied to Mack in another Twitter post: "I miss you."
The question is whether Mack, who is in the final year of his rookie contract, will decide to rejoin his teammates before their opener a week from Monday night against the Los Angeles Rams.
I miss you— Derek Carr (@derekcarrqb) August 31, 2018
Mack will lose game checks of about $800,000 for every regular-season game he misses. The two sides reportedly have not had contract talks for several months.
Teams contacting the Raiders about a possible trade reportedly have been told that Oakland wants at least two first-round draft choices in exchange for the NFL's 2016 Defensive Player of the Year.
There is speculation that the Rams' signing of defensive tackle Aaron Donald on Friday might lead to an end to the stalemate because it sets a new bar for defensive players of that caliber.
Donald, the 2017 Defensive Player of the Year, finalized terms on a contract extension that will make him the highest-paid defensive player in league history, the team announced Friday.
Financial terms of the contract were not released, but Donald reportedly will earn $135 million on the six-year extension. The deal features $87 million guaranteed, including a $40 million signing bonus.