SURPRISE, Ariz. -- Outfielder Joey Gallo is sidelined with a strained right groin muscle and the Rangers are unsure if he’ll be ready for Opening Day on March 28 against the Cubs.

“Hard to say right now,” Rangers assistant general manager Shiraz Rehman said on Sunday. “We hope so…we’ll probably know more at the end of the week."

Gallo felt the muscle while playing against the Royals on Thursday. It still bothered him on Friday, so the Rangers sent him for an MRI. The results showed a “mild” strain.

“I wouldn’t expect to see him in games until the end of the week,” Rehman said. “Give it some time to get healthy. Take it a little slow in Spring Training rather than rushing it.”

Rehman emphasized the Rangers aren’t ready to say Gallo will have to begin the season on the injured list.

“Could go different ways depending on how it looks at the end of week,” Rehman said. “We do know it’s a mild strain. Very optimistic…just a matter of seeing how he responds and how quickly he recovers.”

Also, Rangers first baseman Ronald Guzmán was scratched from Sunday's lineup with a sore left knee. Guzman said he felt the knee tighten up on him during pregame batting practice. The injury is not considered serious.