He was called up because infielder Jonathan Villar remains out of the lineup with a sore left knee from Friday night on a tag play at third base. Villar did appear as a pinch-hitter on Sunday, hitting a grand slam in the fifth inning off Pirates reliever Juan Nicasio.
"We're a little short on the bench, for sure," Brewers manager Craig Counsell said. "[The move is] just to make sure we're covered for these games, and Villar is getting better, he's feeling better today. Rivera is just another player to use.
"It's day to day with Villar, I'm not going to tell you he's going to play tomorrow, but it's day to day."
Rivera appeared in 20 games for the Brewers this season, hitting .204 over 49 at-bats.
George Von Benko is a contributor to MLB.com based in Pittsburgh.