SAN DIEGO -- William Myers made an immediate impact upon his reintroduction to the Padres' lineup Monday night at Petco Park, but his return -- and the good vibes surrounding it -- were short-lived.
Myers homered in his first at-bat after missing Saturday's game with back tightness. But the Padres right fielder exited after the fifth inning with triceps soreness that he said made it difficult for him to throw the ball back to the infield.
After the game -- a 7-4 loss to the Rockies -- Myers underwent X-rays and an ultrasound, and the results came back negative. The extent of the injury remains unclear.
"It's very frustrating," Myers said. "I worked super hard this offseason to play every day, not to come out of any games. It's been tough, but it is what it is. You just keep moving forward and hope to get better."
Myers said the injury arose during batting practice, but it wasn't serious enough to ask out of the lineup. It worsened when he was forced to make a couple throws to the infield. In the fifth inning, Myers' discomfort became plainly visible in right field, as he held his throwing arm at an angle over his chest.
Afterward, Padres manager Andy Green wasn't especially confident Myers would be in the lineup Tuesday. The Padres will call up right-hander Tyson Ross before the game, and if Myers is expected to miss extended time, he could be moved to the disabled list to clear room. First, Myers will be re-evaluated early on Tuesday.
"We'll see how he responds and how he feels coming into tomorrow," Green said.
The Padres skipper initially referred to Myers' injury as an elbow issue, though Myers later clarified that it was his triceps that was sore.
It's the second consecutive game Myers has been forced to leave after raking in the early going. On Friday, he had two hits before his back began to bark. (Myers believes that back issue is squarely behind him.)
On Monday night, Myers went deep off Rockies right-hander Chad Bettis -- a 109 mph missile to the "Beach" section of Petco Park in right-center field. It was his first homer of the season and ninth hit in 17 career at-bats against Bettis.
An inning later, Myers came a foot shy of his second homer. With the bases loaded, he skyed a deep drive to straightaway center, where Charlie Blackmon made a leaping grab just in front of the wall.

Many in the organization view this as a critical year for Myers, who has shown flashes of excellence with the Padres but has too often fallen into prolonged slumps at the plate. Generally, Myers is at his best when he's using the opposite field. Monday's homer was an encouraging early sign.
But that optimism quickly subsided four innings later.
"Hopefully I come back tomorrow and it's gone," Myers said, echoing the wishful thinking throughout the organization.