The move would reunite Walker, a one-time Pro Bowl pick, with quarterback Brett Favre.
Walker's best season came with the Packers in 2004, when he had 89 receptions for 1,382 yards and 12 touchdowns -- with Favre throwing the ball.
The Vikings are in need of depth at wide receiver, with Percy Harvin struggling with migraines and uncertainty surrounding wideout Sidney Rice's return.
Harvin has missed all but a handful of training camp practices, plagued with debilitating migraine episodes that can leave him unable to function.
Harvin was hospitalized last week after collapsing from a migraine episode during practice. He did not travel with the team to San Francisco for Sunday's preseason game against the San Francisco 49ers, but is expected to return to the field Tuesday.
Meanwhile, Rice has been camped out on the Vikings' physically unable to perform list, and has not practiced with the team, limited only to sideline conditioning during training camp. Rice has offered no estimate of when he might return to the Vikings' active roster.
The Vikings also placed WR and punt returner Jaymar Johnson on season-ending injured reserve with a broken left thumb.
Walker, a seven-year veteran, appeared in three games for the Oakland Raiders last season. Oakland released Walker in March 2010.
The Associated Press contributed to this report.