Reddick hyperextended the knee at the beginning of June and missed three weeks with the injury only to aggravate it in Saturday's game, after going 5-for-11 since his return. He underwent an MRI on Sunday morning, the results of which weren't immediately known.
"We feel like he was probably not going to be on a field doing any activity for five days or so, and then there's obviously a period of time where you have to get him ready again," said manager Bob Melvin. "All those things combined, we felt like the best move was to DL him."
Reddick was concerned Saturday night that the pain trumped what he experienced before, but Melvin said the outfielder at least "felt better than he thought he would feel this morning."
"It was still sore and stiff, but he felt better," he continued. "I think it scared him pretty good last night."
With lefty Andrew Heaney going for the Marlins, the A's felt best served to bring in a right-handed bat. Freiman's been swinging a hot one for Triple-A Sacramento, raising his average from .202 to .277 in a span of two months.
Freiman came through with the big hit in Sunday's 4-3 victory, launching a three-run homer.
"I've been feeling good," said Freiman before the win, "Started off slow, but I've put a couple good weeks together. I made a couple adjustments mechanically. My stance is a little narrower, my hands are lower. It's a work in progress, but so far I like it."
Freiman spent the entirety of 2013 with the A's, filling out a platoon with Brandon Moss. He hit .274 with four homers and 24 RBIs in 80 games, including .304 in 148 at-bats against left-handed pitching.
That will largely remain his role.
"I'm thrilled to be here and excited to be back," he said. "It's unfortunate because Josh hurt himself again. I hope he's all right."
It's indeed an exciting time for Freiman, with wife, former LPGA pro Amanda Blumenherst, expecting the couple's first child in November. After dropping her husband off at the airport Friday evening, Blumenherst returned home to pack and caught a Sunday morning flight to Detroit, where the A's head next.
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.