Hughes, who was placed on the 60-day disabled list June 10 after a line drive fractured his left femur, went 1-7 with a 5.95 ERA in 12 appearances (11 starts). He'd also experienced pain in his throwing shoulder, which had caused fatigue in the arm and a drop in velocity.
"It involves the nerves and blood vessels in the shoulder," general manager Terry Ryan said on Tuesday at U.S. Cellular Field. "They'll have to take part of a rib out. This isn't career-threatening, but it's an injury that explains maybe a little bit of his issue. If that is the case, that's a relief."
Hughes, who has three years left on his contract, struggled as a starter this season and was moved to the bullpen prior to being hit with the liner by Miami's J.T. Realmuto in his first relief appearance.
"They kept trying to figure out what the problem was," Ryan said. "They kept looking for issues in that shoulder to explain why he may not be able to have the stamina and the ability to go deep [in games]. They examined for this and detected it, which is good. Now we're going to take care of it, which is good. This will be the end of his year, however."
Brian Hedger is a contributor to MLB.com based in Chicago. This story was not subject to the approval of Major League Baseball or its clubs.