"He's had bumps and bruises along the way, getting hit by a pitch, and having some soreness," Epstein said of Stewart, who is rehabbing with Triple-A Iowa. "We'll just monitor it daily and see what he's doing. He didn't have a Spring Training, so we look at this [time] as Spring Training."
Stewart strained his left quad in an intrasquad game Feb. 21 and did not play in Spring Training.
"There's nothing real good going on with his swing right now," manager Dale Sveum said. "I think he's seeing a lot of pitches and he is taking some walks, but there's no hard contact going on."
In 12 games with Iowa, Stewart was 4-for-40 (.100) with one double and four RBIs. He's struck out 15 times and walked eight times.
"He doesn't have his timing," Epstein said. "He's not been performing that well and his timing isn't there yet. He needs to keep playing."
Stewart does have an option remaining, so he could be activated off the disabled list and then sent to the Minors.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat Joey Nowak contributed to this report. This story was not subject to the approval of Major League Baseball or its clubs.