Wells was scratched from the starting lineup Saturday and wasn't available again on Sunday, according to manager Eric Wedge.
"He's scuffling," Wedge said. "He really got locked up bad. I haven't seen him yet today, but I'm hoping he got some sleep last night. If you've ever been there, that's no fun. It was just one of those fluke things. Backs and necks are tough. There's not much you can do."
Wells is hitting .222 in 80 games with the Mariners this season and Wedge had hoped to use him more in the coming days in order to take advantage of his defensive presence. The 25-year-old is 1-for-9 since being recalled from Triple-A Tacoma earlier this month. He played in six of the first nine games after being brought back, with the last three as a late-inning defensive replacement.
"I was just excited to be back in the lineup," Wells said Sunday. "I took some swings and felt a sharp pain. I thought I could shake it off, but I started getting sharp shooting pains up the back of my neck and couldn't even hold my head up. They said it was maybe an inflamed nerve or something."