USA Today Sports first reported Monday that Ichiro and the Mariners were close to a one-year major league deal.
The Mariners announced earlier Monday that outfielder Ben Gamel will miss four to six weeks with an oblique injury, jeopardizing his availability for Opening Day and opening a potential roster spot for the 44-year-old Ichiro.
Ichiro's deal with Seattle could be completed as early as Monday, the source told Crasnick.
The Mariners were hopeful that Gamel would miss only a few days, but an MRI revealed a more extensive injury after it was reviewed by team physicians. Gamel first felt the injury after batting practice late last week.
Gamel is added to a growing list of ailments for the Mariners, who already have seen first baseman Ryon Healy (hand), outfielder Mitch Haniger (hand) and pitcher Felix Hernandez (bruised forearm) slowed by injuries during spring training. Outfielder Guillermo Heredia is still recovering from offseason shoulder surgery, leaving Seattle thin at the position.
Ichiro was a 10-time All-Star during his 11-plus years with the Mariners from 2001 to 2012. He is the franchise's all-time leader in batting average (.322) and hits (2,533).
The Mariners have not reached the postseason since Ichiro's historic rookie season in 2001, when he was both the American League MVP and Rookie of the Year while leading Seattle to a league-record 116 wins in the regular season.
Ichiro became a free agent when the Miami Marlins declined his $2 million club option for 2018. The move by the Marlins was the start of an anticipated payroll purge by Derek Jeter's new ownership group. Jeter and Ichiro were New York Yankees teammates for 2½ seasons.
Ichiro ranks 22nd with 3,080 career hits but started only 22 games last year and had 196 at-bats, the lowest total of his 17-year career. He set a big league mark with 109 plate appearances as a pinch hitter, and had a franchise record 27 pinch-hits.
Ichiro was batting .202 on July 4 but hit .315 the rest of the way to finish at .255. He became just the sixth player 43 or older to record at least 50 hits.
Ichiro, who has said he wants to play until he's 50, was 27 when he began his major league career. He had 1,278 hits while playing nine years in Japan.
The Associated Press contributed to this report.