© 2014 MLB Advanced Media, L.P. All rights reserved.

5/7/2014 9:05 P.M. ET

Infante's back keeps him out of finale lineup

Royals start Valencia at second base in rubber game at Petco Park

SAN DIEGO -- For a long time on Wednesday morning, no lineup was posted for the Royals.

"We're waiting on Omar," manager Ned Yost said, settling in the dugout as the Royals began batting practice.

That was second baseman Omar Infante who, it turned out, was having trouble getting his back loose after the two extra-inning games against the Padres.

"His back's a little stiff. He's trying to get good and loose," Yost said. "It got stiff after the game."

Yost was waiting for Infante to test his back with some batting practice swings.

But Infante never got loose enough for BP and couldn't go against the Padres. Instead, Danny Valencia got his second start at second base this season. Primarily a third baseman, Valencia's only other start at second came on April 8 against Tampa Bay, the day after Infante was struck in the jaw by a pitch.

Valencia played that day, but Johnny Giavotella was called up from Triple-A Omaha and started at second base the following day. After an open date, Infante returned to the lineup on April 11 and Giavotella was optioned back to Omaha.

But Yost indicated after Wednesday's 8-0 win that Infante could be back in the lineup as early as Thursday and he didn't anticipate having to call up a second baseman.

"His hips got out of line and he got back spasms, which happens from time to time. There's not a lot of concern involved," Yost said. "I look forward to him playing [Thursday], but if it's still tight, we'll give him another day."

Valencia filled in with a 3-for-5 game on Wednesday.

"Danny had three hits, played well defensively, and did a nice job," Yost said.

Duffy heading back to 'pen after Seattle start

SAN DIEGO -- Left-hander Danny Duffy will start for the Royals at Seattle on Thursday night and then go into a state of limbo for a few days.

This will be Duffy's second start in place of fellow lefty Bruce Chen, who's on the disabled list with a bulging disc in his back. But with Monday being an open date, Duffy will be skipped in the next turn of the rotation and then likely will go back into the bullpen for a spell.

Just how long isn't known. Manager Ned Yost has targeted May 17 as a possible return for Chen or, if he's not ready, another start for Duffy.

"He'll pitch [Thursday], then he won't pitch again until the 17th, so he'll probably go in the 'pen once we come back [to Kansas City]," Yost said.

In the interim, Chen will be trying to recover from his back ailment and, if possible, throw in a Minor League rehabilitation outing.

"Then if Bruce is ready to make a start on the 17th, then, we'll make a decision," Yost said.

Duffy began the season as a starter for Triple-A Omaha, got called up to make six bullpen appearances and then was tabbed to replace Chen. Duffy's staying flexible.

"I'll go wherever they want me to go. I'm just happy to be on the team. I did really enjoy the bullpen, though. I learned a lot out of that gig so we'll see what happens," he said.

Duffy's not a guy to covet a particular role.

"I don't really have an ego," Duffy said. "I really don't have any grounds to have an ego. So, I'll go wherever they want me to go."

That's an attitude that Yost likes.

"He really wants to do well and all for the right reasons -- for his teammates, for the team," Yost said. "I'm sure everybody's satisfied when they do well, but he's more satisfied for the team than he is for self-indulgence."

Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.