"It's a situation where we are going to get him in to see the doctor, get an MRI and make sure he's all right. We want this guy to continue to pitch so we're going to be conservative and make sure he's okay. Not push the envelope," said Rangers manager Jeff Banister.
The Rangers have not named a starter for Monday against Oakland. Cesar Ramos could be brought out of the bullpen or the Rangers could call up veteran right-hander Kyle Lohse from Triple A Round Rock.
"I have heard it's common for players that have had Tommy John surgery to have issues like this," Darvish said. "Right now I don't want to push it and make it worse. It's a precaution, we hope it's nothing serious and that I can be back soon."
Darvish left his last start on Wednesday after five innings because of some tightness in the right shoulder/neck area. He was able to throw 21 pitches in a bullpen session on Friday but felt more stiffness on Saturday when he tried to throw again.
Moreland shows muscle:
Mitch Moreland had two home runs on Friday and two doubles on Thursday. It marked only the second and third time this season he has had two extra-base hits in one game.
He went into Saturday night's game with five hits in his last 11 at-bats, giving the Rangers hope he is emerging from an extended slump.
"I'm just trying to go up there and have a good approach, get a good pitch to hit and put the barrel on it," Moreland said. "That's been my goal since the start of the season. Nothing's changed. I'm trying to keep it simple."
• The Rangers are still on hold with third baseman Adrian Beltre, who is sidelined with a strained left hamstring. He took batting practice and did some light jogging but was out of the lineup for the third straight game. The Rangers are holding off putting him on the disabled list.
"We are going to stay patient with a guy who means so much," Banister said.
• Shin-Soo Choo, on the disabled list with a strained left hamstring, was 0-for-3 with two walks in Friday's game for Double A Frisco but was able to play nine innings in the outfield without problem. If he repeats that on Saturday night, he could be activated on Monday in Oakland.
• Banister said the Rangers are still mulling the possibility of using a sixth starter in the next week to give the whole rotation an extra day of rest. The Rangers are in a run of 20 straight games without a day off that runs June 3-22.
T.R. Sullivan has covered the Rangers since 1989, and for MLB.com since 2006. Follow him on Twitter @Sullivan_Ranger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.