The righty reliever, who is in the midst of his third stint on the disabled list this season, got sick and had to be hospitalized.
"He didn't [throw a side session]," manager Terry Francona said on Monday. "You guys are the crack media. He hasn't been there for three days. He had intestinal turmoil. We actually had to send him to the hospital. I think he's having a colonoscopy today just to check some things, so, hopefully, we'll have something pretty soon."
Jenks has been sidelined by upper back woes. Sunday's side session was going to be the first since his latest trip to the DL. Before developing the illness, Jenks was planning on training in Fort Myers, Fla., this week while the Red Sox were on the road. For now, those plans are on hold.
"He got really sick," Francona said. "I mean, really sick."