For now, Oakland would have to trade for Lynch because his NFL rights remain the property of the Seahawks, as he has two years remaining on his contract. Seattle general manager John Schneider and Raiders general manager Reggie McKenzie have a longstanding relationship; they worked together in the Packers' front office.
Under terms of his existing contract, Lynch would be in line for a $9 million salary and cap hit in 2017. In 2018, he would be due a base salary of $7 million and could potentially earn an additional $3 million roster bonus.
Seattle could ultimately decide to release Lynch for the sole intent of having him sign with Oakland. In that scenario, Lynch would be free to negotiate a new deal with the Raiders.
"It could really happen," one source familiar with the situation said Friday.
Lynch, who will turn 31 in April, also must decide whether to resume his NFL career. It's an idea he has considered, according to sources. Playing for his hometown team would be an incentive and could influence a decision.
Over the years, sources told ESPN's Adam Caplan, Lynch told people his dream was to play for the Raiders. He has a "Beast Mode" apparel store in Oakland.
The Raiders have interest, and it's not just in Lynch, after Latavius Murray signed with Minnesota during free agency. Free agent Adrian Peterson, who likes the team's playoff potential, also remains a possibility for Oakland, sources told ESPN.
In his nine-year career, Lynch started 114 games and carried the ball 2,144 times for 9,112 yards (4.3 yards per carry) and 74 touchdowns.
Asked last June if he was fine with never playing another down, Lynch said, "Oh yeah, I'm good. I enjoyed my time."
Offensive tackle Russell Okung, Lynch's teammate for six years with the Seahawks, endorsed the idea of a comeback.
"Marshawn is a mastermind," Okung told ESPN's Jim Trotter. "If he has been thinking about this all along, it would be great."
Lynch retired after the 2015 season. "I thought it was way too early," Okung said. "He is one of the best talents I have ever seen. I think he can play as long as he wants to play. There's nobody that's better than him and I'd love to see him back ... in a Chargers uniform."
Okung signed a four-year deal with the Chargers last week.
The 2015 season was a struggle for Lynch. He missed nine regular-season games and one in the playoffs after undergoing surgery associated with a sports abdomen injury on Nov. 25. Lynch had missed just one game the four previous seasons.
Lynch was among the most productive running backs in the league during his time with the Seahawks, who acquired him in a midseason trade with the Buffalo Bills in 2010. During his five seasons in Seattle, Lynch was third in rushing yards (5,774), second in first downs (294) and first in rushing touchdowns. His 51 touchdowns during that span surpassed Peterson's second-place total by six.
Seattle played in the Super Bowl twice, winning once, during Lynch's time there.
ESPN's Sheil Kapadia contributed to this report.