No decision has been made on who will replace him in the Royals' rotation. He was scheduled to start Sunday in Chicago, but given Thursday's open date, Danny Duffy will move up and start that game instead on a normal four days' rest. Bruce Chen will start on Monday night in Texas, so a fifth starter won't be needed until Tuesday night against the Rangers.
"I'll look two days before that and see who's available, between [Luis] Mendoza, [Nate] Adcock and [Vin] Mazzaro," manager Ned Yost said.
All three are currently in the Royals' bullpen as long relievers.
Sanchez said that he'd had problems with the bicep his last two starts.
"It's normal," he said. "I have it every year. I just get it and it's no big deal."
On Monday night, Sanchez lasted just three-plus innings before being taken out of an 11-5 loss to the Red Sox. He is 1-2 with a 6.75 ERA in six starts.
"It was lingering bicep tendinitis in his left arm, the same thing he had in Spring Training a little bit and it was starting to get progressively worse," Yost said. "Tendinitis not only affects the velocity on your fastball, it affects your command, and we need him to be the pitcher that we all know that he is."
The move cuts the pitching staff from 13 to 12, a number which Yost prefers, because with infielder Johnny Giavotella called up from Triple-A Omaha, it gives him a deeper bench.
Yost will have another pitching decision to make at the end of this week or early next week, when reliever Greg Holland is expected to return from his rehabilitation assignment.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.