Then there's Shawn Hill, who's scheduled to start on Thursday against the Phillies. Hill has battled injuries and recently suffered from a strained left shoulder.
Nationals manager Manny Acta was asked about the possibility of carrying 13 pitchers.
"Not right now," Acta said. "I'm taking a look at it."
However, general manager Jim Bowden is trying to change his manager's mind.
"I'm a 13-pitcher guy with our team," Bowden said. "[Acta] does not want to. I'm not going to hamstring Manny if he does not want to go to 13. I am going to keep fighting for 13."
The first decision on the pitching staff will likely occur with King.
"I feel good," King said after his simulated game. "I feel like everything went well."
Acta said he was pleased with King's effort.
"He felt good," Acta said. "We're going to wait a day and then we'll make a decision. We'll see how he bounces back."
As for Ayala, Bowden is cautiously optimistic.
"He got up to 89 [mph]," Bowden said. "He only threw nine pitches. It was a very good outing. I'm not going to put a timetable on it. Certainly, he's made significant measurable progress."
Feeling better: Hill said he's healthy and looking forward to Thursday's start against the Phillies.
"I feel good," Hill said. "My shoulder feels strong and I'm ready to go."
Hill is 1-2 with a 2.92 ERA this season.
"He's fine," Acta said of Hill. "It is like we've said all along. This guy is just about being healthy. If he's healthy, he's going to give us a good chance every five days."
Message received: Bowden is happy with how center fielder Ryan Church has responded since he was benched on Sunday by Acta for not hustling on a ground ball in the second inning.
"I thought it was a great message," Bowden said. "As Ryan told me, 'Message received.' It won't happen again."
More help on the way: Center fielder Nook Logan (strained left foot) and shortstop Cristian Guzman (strained left hamstring) are expected to re-join the Nationals very soon.
"Nook, I hope, is ready to play soon, hopefully Sunday or Monday," Bowden said. "I expect [Guzman] to play soon. I think he'll be ready in four to five days."
On the comeback trail: Third baseman Ryan Zimmerman entered Tuesday's game hitting just .241 with one home runs and eight RBIs.
It's well off last year's pace, when Zimmerman hit .287 with 20 homers, 110 RBIs and finished second in the National League Rookie of the Year balloting.
"He's going to be fine," Acta said. "If he struggles for a longer period of time, maybe we'll step in and do something else."
Zimmerman has started to come out of his slump, hitting safely in seven straight games (11-for-33) with two doubles, one home run and six RBIs.
Coming up: Right-hander John Patterson (0-3, 7.00 ERA) will oppose Philadelphia's Jon Lieber (0-0, 3.38) in the second of a three-game series on Wednesday at 7:05 p.m. ET. This will be the fifth start of the season for Patterson.