SEATTLE -- Marco Gonzales on Monday took the most significant step yet in his rehab from a left forearm strain that has sidelined him nearly one month.

The Mariners’ No. 1 starter threw off a mound for the first time since his most recent start in Houston on April 27, when he said he first experienced the forearm issue during the sixth inning. He tossed roughly 15 light throws to a catcher that stood in front of home plate, and he will continue to lightly throw throughout this week, aiming for his first full intensity bullpen session on Friday. He’s been throwing with Ichiro Suzuki throughout his rehab.

Though Monday represented a minor milestone, the 29-year-old veteran estimates that he’s at least a few weeks away from pitching in a live game, which will likely begin with a rehab assignment.

After the Houston start, Gonzales and the Mariners sent his MRI results to Dr. Neal ElAttrache, the renowned surgeon who performed Gonzales’ Tommy John surgery in 2016, who responded positively to the results.

Gonzales, who has also dealt with pectoral and neck issues in the distant past, has been the headliner of Seattle’s beleaguered starting pitching staff, which is down four arms since Opening Day. The club has used his turn through the rotation as a bullpen game, including Sunday’s 3-2 win over Cleveland.

“I feel like I kind of hang the bullpen out to dry a little bit with the bullpen day that we’re going forward with,” Gonzales said. “Sitting and watching, it's frustrating. But I've been through my fair share of injuries before and the way to get through it is to take it day by day and not let the frustration overcome you at all and try to channel it into the exercises and workouts and unfortunately, I've gotten good at that.”

Because of Thursday’s off-day, the Mariners will be able to re-slot their rotation and avoid a ‘pen day this next time through. But given Gonzales’ timeline, it’s likely that they’ll need to use that strategy again soon. Robert Dugger, who tossed three shutout innings Sunday to outduel Shane Bieber, will likely make those starts, Mariners manager Scott Servais said.

Mask mandate lifted for vaccinated fans

Fully vaccinated fans attending games at T-Mobile Park are no longer required to wear masks, beginning with Monday’s series opener against the Tigers. This change aligns ballpark protocols with the recently announced CDC and state of Washington guidelines for fully vaccinated individuals.

Fans who show proof of vaccination will receive a wristband that verifies that they are permitted to go mask-free while in the ballpark, which can be obtained when they enter through the center- or right-field gates, or when they check in at the vaccine-only seating sections.

Fully vaccinated is defined as at least 14 days past the final dose of a two-dose vaccine or the single-dose Johnson & Johnson vaccine, and the following will be acceptable as proof of full vaccination:

• Vaccination card which includes the name of the person, type of vaccine and date of last dose

• Photo of a vaccination card as a separate document or on a mobile device

• Documentation of vaccination from a health care provider’s electronic health record or state Immunization Information System record.

Bishop claimed by Giants

Fan and teammate favorite Braden Bishop’s time with the Mariners has come to an end, as the former University of Washington standout was claimed off waivers by the Giants on Monday. Bishop was designated for assignment on Thursday.

This new opportunity in San Francisco will pair him in the same organization as his younger brother, Hunter, who was the club’s No. 10 overall pick in the 2019 Draft and is currently at High-A Eugene. The elder Bishop was a third-rounder in ’15 and a touted prospect, but he couldn’t quite find his footing offensively at the Major League level, where he’s a .133/.188/.156 hitter in 47 games.

During his seven seasons in the Mariners’ organization, Bishop earned the respect of his teammates and coaches for his strong work ethic and attitude, especially after the passing of his mother, Suzy, in 2019 due to Alzheimer’s. Before she passed, Bishop established the 4MOM Charity to unite professional athletes, coaches, patients, caregivers and the community in the fight against the disease.

Other roster moves

• Reliever Brady Lail was recalled to give the Mariners a fresh arm after Sunday’s seven-pitcher bullpen game.

• Infielder Jack Mayfield was optioned to Tacoma in a corresponding move.

• Reliever Domingo Tapia was designated for assignment. He made just two appearances and had an oblique setback in Spring Training that curtailed his chances of breaking camp.