A position player will likely be added when Ramirez is optioned back to Tacoma after his Sunday start, with outfielders James Jones or Michael Saunders the likeliest options. Saunders is on a rehab stint from a strained oblique but has played only three games.
Ramirez will fill a spot that opened when the club pushed Felix Hernandez back to Monday to get an extra day of rest and then face a Blue Jays squad that is fighting Seattle for the final American League Wild Card berth.
Ramirez, 24, started the season in Seattle's rotation before being sent down to Triple-A Tacoma after going 1-3 with a 6.75 ERA in five starts. But he's since been called up various times for spot starts, and this will be his fifth time back with the club, having posted a 1-5 record and 4.35 ERA in 12 outings.
Ramirez threw seven innings of two-run ball with 10 strikeouts in his most-recent return in a 3-1 loss to the Mets on July 22. He's gone 3-5 with a 3.76 ERA in 12 starts for Tacoma.
"He threw the ball good and hopefully he has that type of command again," McClendon said of the youngster's last outing in Seattle. "If he does, we have a good chance of winning the game. He's thrown pretty good down [in Tacoma]. Not great, but he's held his own."
The Mariners currently have only four other starters on their 25-man roster, having sent Roenis Elias down after his outing on Thursday. But Ramirez figures to get just the one spot start and return to Tacoma again, as the club can go with a four-man rotation with an off-day coming up Thursday.
Seattle won't need a fifth starter until Aug. 19 in Philadelphia, at which point Elias will be eligible to return since he'll have exceeded the 10-day minimum requirement for a player sent down to the Minors.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.