Yost said he wasn't sure if the cold conditions on the road trip were holding Karns, 30, back from his progression.
"Hard to say but you just have to deal with it," Yost said.
Karns, a longtime starter, will go to the bullpen when he is activated.
Slow start for Soler The Royals had been hoping to get Jorge Soler somewhere near 500-600 at-bats this season. But Yost also has been trying to get all his position players some playing time early in the season, which is why Ryan Goins started at second base, pushing Whit Merrifield to right field in Soler's spot.
Soler also has yet to get his first hit in 2018, going 0-for-11. Yost said he hasn't seen any specific issues in Soler's swing.
"I haven't seen anything [offensively] from anyone," Yost said. "You can't even answer that question with what we've been through, with the weather and [postponements] and everything."
But, Yost has been impressed with what he has seen from outfielder and leadoff man Jon Jay, who was hitting .333 through five games and had drawn four walks.
"You go back and look at his track record and most of [what we heard] is right on," Yost said. "He's always been a .280 or .290 hitter [.289 lifetime]. He gives you what's called a solid professional at-bat."