Escobar took an impact test on Friday and while the results weren't in yet, Yost said, "He's going to fail it."
"He still has some issues," the skipper said. "He looks great and feels great, but his motor speed and motor skills ... he didn't fare well in that.
"Even though he feels good, his reaction time is down. This is something that could end your career. This isn't something you play with. I saw it end Corey Koskie's career in Milwaukee on just a benign ball where he dove it for it, injured his head and never played again."
In 2006, long before adequate concussion tests really existed, Koskie fell backward while trying to catch a popup. Though Koskie didn't actually hit his head on the ground, he began feeling disoriented. His condition worsened over the following months and he never played for the Brewers again.
Koskie tried to make a comeback with the Cubs in 2009, but he retired that spring.
The Royals won't take any chances with Escobar.
"The percentages are high it could get worse if [you rush back]," Yost said. "Just take the five days and let it heal. It's not worth it."
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.