Manager Clint Hurdle said he did not know the specifics on how long Walker would be sidelined, but acknowledged the lineup would take a hit without him.
"We've encouraged him to stay mentally strong, to do what he's able to do when he's able to do it," Hurdle said. "This could very well -- based on his makeup, his focus -- turn out to be a blessing in disguise."
This is Walker's third DL stint in the last 13 months. He was sidelined twice last season, once in May with a laceration on his right index finger and again two months later with a strained right oblique. He also sat out nearly three weeks near the end of the 2012 season with tightness in his lower back.
Polanco filled Walker's spot on the 25-man roster and also will take over his place in the order, as the right fielder is slated to hit second Tuesday against the Cubs. On the field, Hurdle said Josh Harrison will fill the second base void most of the time while Walker recovers, but utility man Clint Barmes is starting there Tuesday.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer. Stephen Pianovich is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.