Warren initially felt the pain Tuesday playing catch and pitched through it in Anaheim, but he didn't feel right as he was pitching. When there continued to be discomfort, he told the team Thursday and went through tests.
Warren, who has never been placed on the DL before Friday, has been one of the best pitchers in the Yankees' bullpen this season, carrying a 2.23 ERA across 32 1/3 innings, including a WHIP of 0.80. The initial plan was to rest him over the weekend in Oakland, but the other injuries forced the move.
"I felt like it would be just a few days, and we were going to try to avoid the DL," Warren said. "But last night happened, and they felt they'd have to make a move. … The bright side is I don't feel like I have to rush back in two or three days."
Yankees manager Joe Girardi added, "We're strapped. But we don't anticipate it being more than a 10-day DL, and we think we'll have him back on our next homestand."
In addition to Warren, the Yankees optioned right-handed reliever Giovanny Gallegos to Triple-A Scranton/Wilkes-Barre, making room for catcher Kyle Higashioka and outfielder Mason Williams. The two flew in from Buffalo, where the Railriders were about to begin a series, and arrived at the ballpark Friday afternoon.
Williams was in the starting lineup for Friday's game against the A's, partly because Girardi told outfielder Brett Gardner and infielder Didi Gregorius they would be getting the day off. But Girardi is still confident in him despite the long travel.
"He's a tremendous defender, and with us, he's had good at-bats," Girardi said. "He was on a really long flight today, but he's in the lineup, so go get them."
Sanchez and Hicks are both day to day, and Girardi said the team was encouraged that neither player felt worse when they woke up Friday morning. Both will not play tonight unless there's an emergency, but Girardi is hopeful they can avoid the DL.
• Aroldis Chapman (left shoulder rotator cuff inflammation) threw 20 pitches in a rehab appearance for Double-A Trenton, throwing nine strikes in two-thirds of an inning. He walked two, struck out two and threw two wild pitches. He's expected to fly to Oakland tomorrow and be activated Sunday.
• With the bullpen down to seven men, right-hander Luis Cessa is available in relief after being called up Thursday. If Cessa isn't used tonight, Girardi said it's likely he will start Saturday and Masahiro Tanaka's start will be bumped back to Sunday. But if Cessa throws Friday, Tanaka will start Saturday.
Alex Simon is a reporter for MLB.com based in the Bay Area. Follow him on Twitter at @alexsimon99. This story was not subject to the approval of Major League Baseball or its clubs.