Wiemer, 24, was the Brewers' starting center fielder for much of the season. He played quality defense and helped Milwaukee withstand the loss of fellow rookie Garrett Mitchell, who opened the year as the primary center fielder but has been out with a shoulder injury since mid-April. Mitchell began a rehabilitation assignment with Nashville on Friday.
Wiemer has struggled over the past month, and his playing time dipped after the National League Central-leading Brewers promoted rookie Sal Frelick and acquired Mark Canha at the trade deadline. Wiemer is 2-for-28 with 12 strikeouts over his last 14 games.
"When Sal got here, Joey's playing situation changed, and that's been different for him," Milwaukee manager Craig Counsell said before the Brewers' 9-5 victory Saturday night over the Washington Nationals. "He has not been in there every day, and that's been harder for him, I think. That's just part of it. That's another adjustment that a young player has to make. You want those adjustments to happen overnight and very quickly, and they don't always happen that way."
Wiemer is batting .204 with a .283 on-base percentage, .362 slugging percentage, 13 home runs, 42 RBIs and 11 steals in 132 games this season.
Perkins, 27, is hitting .212 with a .311 on-base percentage, two home runs, 16 RBIs and five steals in 56 games. He had gone on the injured list Aug. 11 with an oblique issue.