SURPRISE, Ariz. -- As the Royals gear up to break spring camp a week from Sunday, it appears more and more likely that left-hander Danny Duffy, who is overcoming a bout of shoulder tightness, will stay in Arizona for extended Spring Training to continue to build up arm strength.

Manager Ned Yost said no decision has been made regarding Duffy and a possible stint on the injured list.

“I imagine it’s an option,” Duffy said. “I don’t foresee it as a very lengthy stay. Obviously, no one wants to stay here, but you have to handle business.

“I haven’t heard that it would be lengthy.”

Yost has indicated previously that he wouldn’t need a fifth starter until the second week of the regular season, at the earliest.

Duffy could then take his time building his arm strength up.

“It buys me time to get ready,” Duffy said.

Duffy, who felt tightness in his shoulder about two weeks ago, is continuing to progress in his throwing program. He threw about 35 pitches Saturday on the side, including several changeups.

“I don’t think it’s a huge task to get built up,” Duffy said. “My last 10-15 pitches today were the hottest. My extension was good. Everything was coming out good. Today was another good step.

“We’ll do another bullpen, and then maybe a live bullpen or two and we’ll go from there.”

Could Duffy appear in a Cactus League game late next week?

“Maybe. I’m not sure,” he said. “I don’t really know what the plan is, but the impression I get is they just want me to get right. If I’m not right, I’ll have a year like I did last year and we don’t want that.”