Lowe was hit in the left foot by a line drive on Saturday night against the Athletics and was on crutches Sunday. The Mariners opted to send him down to Tacoma rather than put him on the disabled list for strategic reasons.
"Because we think that he will be able to pitch before that DL time is up, and we can bring him back much earlier this way," the manager said. "When rosters expand on [Sept. 1] we can bring him back."
Riggleman also said the move doesn't cost Lowe, who has been with Seattle all season, any service time because he will be down for such a short span. He also said he hopes Lowe will be able to pitch in Tacoma in a few days before he comes back up.
Messenger was released from the Giants on July 9 (at his own request) and was signed by the Mariners as a Minor League free agent on July 10. He had a 4.83 ERA while with San Francisco's Triple-A Fresno team, but in 12 relief appearances in Tacoma, he has gone 6-0 with a 2.38 ERA.
The big right-hander has spent some time in the Major Leagues with the Marlins and Giants during the past three years, but this is his first time up to the big leagues this season.
Messenger said the Mariners actually called him on Aug. 1 -- the day of his first child's birth -- to see about bringing him up, but there were some minor complications that made it not possible. The team ended up promoting lefty reliever Jake Woods to the big club on Aug. 2.
"My wife had some complications afterward and the baby [a girl named Francesca] had some. But everything is good now and everybody is healthy and you can't ask for anything better," he said. "I'm back to where I want to be."
Messenger said he "just didn't feel things were right over there" in San Francisco.
"These guys were willing to give me an opportunity, and I came over here and things have been good ever since," he said.
Riggleman said he didn't know much about Messenger, but that he figures to start in long or middle relief.
Jesse Baumgartner is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.