ST. LOUIS— Royals left-hander Danny Duffy threw four solid innings in a rehab start at Triple-A Omaha on Tuesday, and he’s scheduled to throw again on Sunday with a pitch limit of 65.

And as Duffy continues to build up his arm strength, the Royals can delay what will be two very difficult decisions to make when Duffy is ready: Who goes off the 25-man roster? And who gets bumped out of the rotation?

The decision likely will be postponed for almost two weeks. Kansas City wants to make sure Duffy, who is on the disabled list with biceps tendinitis, is up to 100 pitches in his rehab assignment before activating him, and he isn’t scheduled for that workload until June 24.

Earlier this week, manager Ned Yost said Duffy definitely would return to the Royals’ rotation when he is healthy and ready.

On Wednesday, Yost modified that stance slightly.

“Yeah. I mean, he has got to throw good,” Yost said. “If he’s not, I’m not putting him back in the rotation. But if he’s throwing good, which I fully expect him to do, he goes back in.”

First, someone will have to come off the roster, and that will have to be a pitcher, since Kansas City is carrying the minimum number of backup positions players -- a reserve catcher, outfielder and infielder.

“It’s tough, because we don’t have anyone with options,” Yost said.

Long reliever Joe Blanton has pitched well -- 2.19 ERA in six games -- but the Royals won’t need an extra long man when Duffy returns, because one of the starters will likely then assume that role. Blanton would seem to have pitched well enough to attract some trade value.

The really hard decision will be determining which starter gets bumped among Jeremy Guthrie, Jason Vargas and Chris Young, all of whom have pitched well lately.

Young started the season as the long man, but he has been phenomenal as a starter -- he is 5-2 with a 2.25 ERA and twice has taken no-hitters through five and 6 1/3 innings.

Yost said he has “a plan” for the decision process, but he isn’t about to reveal it to reporters.

“We got a lot of options, and I’m not talking about any of them right now,” Yost said. “I’m not speculating on things way down the line that involves players in that room. Nah. We don’t do that. There are lives in there, so we don’t speculate.”