NEW YORK -- The Yankees may finally have an explanation for Luis Severino's sophomore slump. Forced to leave his start in the third inning on Friday, the hurler has been diagnosed with a mild strain of his right triceps, which landed him on the 15-day disabled list.
The Yankees called up right-handers Chad Green and Conor Mullee from Triple-A Scranton/Wilkes-Barre on Saturday morning. In addition to putting Severino on the DL, they optioned catcher Gary Sanchez to Scranton/Wilkes-Barre and transferred righty Bryan Mitchell and infielder Greg Bird to the 60-day DL.
Severino struggled mightily in a 7-1 loss to the White Sox, surrendering seven runs and seven hits with four walks before leaving the field with head athletic trainer Steve Donohue. An MRI taken during the game revealed the strain.
"You worry about it, because we've seen a lot of guys in the game of baseball have to go on the DL," Yankees manager Joe Girardi said.

The Yankees said that Severino will not pick up a baseball for five to seven days. Girardi said that Severino "just kind of looked funny" shaking his right arm after his 81st and final pitch, a 95-mph fastball to Jose Abreu.
Catcher Austin Romine said that he did not notice anything was awry during the outing, except for Severino's command.
"He's kind of a bulldog out there," Romine said. "He's not really going to give in or say that he wants to come out. He's going to keep pitching when he wants to pitch. He's going to keep grinding. That's what he did. It comes down to the execution of pitches. We were kind of missing."
Severino was thumped for three runs in the second inning, allowing a run-scoring double to Alex Avila and a two-run Abreu single, then could not record the final out of the third inning.
Adam Eaton stroked a two-run double, Jimmy Rollins connected on a long two-run homer, and one pitch later Severino was headed for an MRI tube.
"He had no command, he was not throwing the baseball where he wanted," Girardi said. "He walked guys, he left balls up, he missed spots. No command."
The Yankees had high hopes after Severino showed great poise in his first 11 Major League starts, promoted last August as he helped the club return to the postseason.
That success has not carried over to the new season, as Friday's outing swelled his ERA from 6.12 to 7.46 -- the worst out of 103 qualified Major League starters this season. The Cardinals' Adam Wainwright has the next highest ERA, at 6.80.
Despite that, the Yankees had been reluctant to send Severino back to the Minors, having seen signs of improvement as he struck out nine over 6 2/3 innings against the Red Sox last week. Yet he seemed to be teetering on the brink of a demotion, with left-hander CC Sabathia preparing to rejoin the rotation during the club's upcoming West Coast road trip.
Worth noting
• Girardi said the reason Sanchez, the Yankees' No. 3 prospect, was optioned a day after he was called up was because Girardi didn't want to lose Nick Goody from the bullpen. Goody wasn't available in Saturday's game after throwing 3 1/3 innings Friday following Severino's early exit.
"Our plans were to DH Sanchez today and possibly do something after that," Girardi said. "When you send a player down, he's gone for 10 days. Goody has thrown the ball pretty good. So we felt that ... 10 days, one day is a sort of big. So we decided to stick with Goody."