The Mariners optioned Tomko, 26, to triple-A Tacoma on Sunday as they reduced their roster to 25 players.
They also optioned right-hander Kevin Hodges and infielder Carlos Hernandez to their triple-A affiliate. Right-hander Todd Williams also was sent to Tacoma.
Tomko, who was acquired by the Mariners on Feb. 10 along with Mike Cameron and two minor league prospects from Cincinnati for Griffey, told the Mariners he wanted to be traded to the Reds.
While Cameron has been impressive as Griffey's replacement in center field, Tomko has not done well on the mound.
Tomko was bothered by a sore left Achilles tendon all spring. He was 0-2 with a 6.59 earned-run average in three starts and 13 2/3 innings.
"He hasn't pitched over four innings," said Pat Gillick, the Mariners' general manager. "We want him to get some work and get stretched out. We didn't think he could do it here working out of the bullpen. So we want him to go down there and start. We project the guy as a starter. We thought coming into spring training, he'd be one of our starters."
Gillick said he wasn't sure when Tomko would be recalled.
"It depends on how he pitches," Gillick said. "It depends on how the people pitch here and how he pitches in Tacoma."
Tomko politely refused to discuss his demotion with reporters.
"It's not a good time right now," he said.
The New York Yankees purchased the contract of outfielder Roberto Kelly from triple-A Columbus, and assigned outfielder Felix Jose, infielder John Zuber and catcher Chris Turner to Columbus.
Right-hander Darrel Einertson was optioned to Columbus, right-hander Domingo Jean was reassigned to double-A Norwich, and right-hander Mike Buddie was designated for assignment.
Left-handed reliever Pedro Borbon and the Toronto Blue Jays agreed to a $3.2 million, two-year contract extension.
Borbon, 32, joined the Blue Jays as part of the off-season deal that sent Shawn Green to the Dodgers for Raul Mondesi.
Borbon was 4-3 with one save and a 4.09 ERA last year.
The Baltimore Orioles sent outfielders Wayne Kirby, Derrick May and pitcher Rich Negrette to triple-A Rochester.
The Orioles also placed catcher Greg Myers on the 15-day disabled list because of a strained right hamstring and purchased the contract of catcher Willie Morales.
Left-hander Justin Thompson was put on the 15-day disabled list by the Texas Rangers as he continues to be on the mend from a torn labrum in his left shoulder, a move retroactive to March 25. Thompson was part of the nine-player trade that sent Juan Gonzalez to Detroit in November.