Iwakuma, 34, is expected to throw about three innings and 45-50 pitches in the 6:05 p.m. PT game against Eugene at Everett Memorial Stadium.
With Triple-A Tacoma currently on the road in Albuquerque, the Mariners chose to bring Iwakuma back at nearby Everett, which opened its season Thursday. Manager Lloyd McClendon said if all goes well, he expects Iwakuma would make his next rehab start for Tacoma, which returns home next week.
But with the 2013 All-Star sidelined since April 20 when he felt soreness behind his shoulder in his third start of the season, McClendon isn't ready to speculate on how many rehab starts Iwakama will need to make before rejoining the Mariners.
"One at a time," McClendon said. "We'll see where it takes us."
• The Mariners continue to wait for a doctor's clearance before left-hander James Paxton begins throwing. Paxton has been on the 15-day disabled list for three weeks with a strained tendon in his left middle finger, an injury similar to one that sidelined Indians ace Corey Kluber for a month in 2013.
"There's nothing new, other than the fact we have to be patient with this type of injury. We can't rush it," McClendon said. "I spoke with [Indians manager] Terry Francona on that. He said the biggest mistake any of us can make is to rush the pitcher back with that type of injury. Those tendons in that finger area are very tricky."
• Third-base coach Rich Donnelly, who missed Thursday's game after being hospitalized for the second time in the past week to deal with a urinary tract infection, rejoined the Mariners on Friday and resumed his normal duties.
• Edwin Martinez, a 19-year-old right-hander on the Mariners' Dominican Summer League team, received a 72-game suspension Friday for violating the Minor League Drug Prevention and Treatment Program. Martinez was suspended without pay after testing positive for metabolites of Stanozolol, a performance-enhancing substance.
• Left-handed reliever David Rollins, the Mariners Rule 5 Draft pick, gave up two hits and a walk, but no runs, in his first appearance with Triple-A Tacoma on Thursday. Rollins is serving an 80-game suspension for a failed drug test in the spring. He can pitch for Tacoma for 16 days on a rehab stint, then Seattle must decide whether to add him to its 25-man roster on July 4 or offer him back to the Astros, per Rule 5 rules.