Then they optioned him to Class-A Inland Empire.
To make room on their 40-man roster for Guerrero, the Mariners designated outfielder Kenny Kelly for assignment.
Guerrero is the cousin of Montreal Expos All-Star outfielder Vladimir Guerrero.
He spent the last six seasons in the Brewers' organization after signing as a nondrafted free agent in August 1997.
Guerrero appeared in 34 games between Double-A Huntsville and Class-A High Desert this season.