Dayton Dragons starting pitcher Robert Stephenson was in agony.

Not from the strained hamstring he suffered a month ago that landed him on the disabled list until July 8, but from not playing.

Stephenson, the Cincinnati Reds’ first-round draft pick in 2011 and the top pitching prospect in the organization, had not taken an extended break due to an injury in his career, other than a couple of days he didn’t pitch in extended spring training in 2012 due to a forearm bruise. The self-professed baseball addict didn’t like the vacation.

“A month off nearly killed me,” Stephenson said.

Scouting services have described Stephenson as almost “too intense,” a problem minor-league coaches and instructors — who often juggle different personalities and lackadaisical players — are more than happy to deal with. He is also armed with a fastball that has hit 100-mph on scoreboard radar guns across the Midwest League this season.

The Reds have built their pitching staff primarily through scouting and the draft. Homer Bailey and Mike Leake are former first-round draft picks. Tony Cingrani was picked in the third round while Johnny Cueto was an amateur signee. With the inevitable cycle of contracts and free agency, the farm system is more important than ever, especially when it comes to pitching.

Which is why Stephenson is seen as such a key part of the Reds’ future.

“He’s absolutely important,” Reds scouting director Chris Buckley said. “He’s a first-round pick and he’s done very well to this point. We want to make sure he stays healthy.”

Health hasn’t been the only obstacle for Stephenson. He spent the offseason working on perfecting his change-up and curveball. He posted an ERA around 4.00 in April, but he found his groove in May. In his last six starts prior to Monday, Stephenson was 4-0 with an 0.93 ERA. He struck out 50 and walked five in 38 2/3 innings.

By May, Stephenson had found command of his change-up and curveball while changing his fastball from a four-seam to a two-seam. The change made his velocity jump.

“You put those factors together, along with the ability to throw strikes and throw hard — those last few games were very dominant,” Dayton pitching coach Tony Fossas said.

Dominant enough that Baseball American ranked Stephenson second on a list of “Who’s Hot” prospects in May, a list that comprised the entire minor leagues. Dayton manager Jose Nieves, who played with Kerry Wood as a member of the Chicago Cubs, said the pitchers have similar tools.

“I played with the Cubs and I played with Wood and I can see the resemblance,” Nieves said. “For his size, (Stephenson) has more power in his arm. Now that he’s getting a better feel for his breaking pitches, he can get better.”

When and whether Stephenson gets promoted is the big question. He doesn’t know. Neither does Nieves, who has said he thinks he could succeed in AA.

“That’s for the big guys to decide,” Nieves said. “For our sake, I hope he stays here.”

Stephenson said: “I don’t know what their plans are — all I know, I just want to go out there and pitch.”

Whether he has a major-league future depends on his continued progress and health.

“He has to stay healthy and he has to pitch a full season,” Fossas said. “After that, it’s about increasing the number of pitches he throws. In two or three years, we will know.”