Joe Ross. (Photo by Mitchell Layton/Getty Images)

The Nationals will soon face a decision. Stephen Strasburg threw a bullpen session on Wednesday, two days after making his second, and perhaps final, rehab start in recovering from an oblique strain. If Strasburg has no issues on Thursday morning, he could slot back in the rotation, and be ready as soon as Saturday to start again in the majors.

Doug Fister is scheduled to start next on Saturday. Fister has a track record but has struggled to the tune of a 4.86 ERA since he returned from the disabled list on June 18. Rookie Joe Ross was called up for a second stint in the majors to take Strasburg’s spot in the rotation while he was on the disabled list. Ross has been one of the pitching revelations of the Nationals’ season, posting a 3.00 ERA along with poise beyond his years in six starts.

A complicating factor to the entire equation: Ross is only 22 and has never thrown more than 122 innings in any professional season of his career. The Nationals, who acquired Ross in an offseason trade, have taken a conservative approach with young pitchers, not simply ones returning from injury. And the Nationals have acknowledged that Ross, who is healthy, will have to be capped at some point this season.

[There is clearly something wrong with the Nationals]

“Right now, he’s capable but it’s uncharted territory,” Manager Matt Williams said. “So I think it’s going to get to a point where he’s been to an innings total that he’s never been to before. We’ll have to monitor that as we go.”

So far, Ross has thrown 76 innings in the minors and 39 in the majors for a grand total of 115 innings over 20 starts. Last season, he logged 121 2/3 innings between high-Class A and Class AA. Knowing Ross would be limited this season, the Nationals capped his starts at Class AAA Syracuse to five innings before this current second stint in the majors. They wanted to keep him on schedule, but still have him ready for the majors just in case of Strasburg.

“It’s definitely understandable,” Ross said. “I’ve never thrown more than 120 or something innings in a season. Most of the starters here are close to 200 at the end of the year, or around 180. So it make sense. I’m obviously going to want to keep throwing. But if it gets to a point where they’re going to minimize my innings or end up shutting me down, it’s probably going to be for the best. But I’ll deal with that when time comes to it.”

The general rule of thumb for some teams across the league is a 25-30 percent increase in innings from one season to the next for young pitchers. The Nationals consider that a rough outline, too, but obviously that varies depending on many individual factors such as the stress of the innings, the number of pitches thrown, any unknown past injuries, the way a pitcher is throwing or fatigue. Each pitcher is different.

Using the 25-30 percent concept as a guideline, Ross’ cap could be somewhere around 153 innings (a 25 percent increase) and 159 innings (a 30 percent increase). And if Ross is averaging about 6.5 innings per start so far in the majors, he could have about five (conservative) to seven starts left in the season. In other words, about the rest of the month. But if he is limited to five innings per start as he was in Syracuse before his second stint in the majors, he could last deeper into September.

“After one of my starts, after my first stint here, someone asked me how I felt the day after my game,” Ross said. ” ‘I don’t feel too bad.’ [They said,] ‘You know why? Because you’re in the big leagues.’ Which made me laugh. It’s probably true. I feel really good.”

[‘Janssen to Storen to Pap’ has a nice late-inning ring to it]

Ross’ next start is Thursday against the Diamondbacks and he could match last season’s total with a seven-inning performance. As he nears that number, Ross has learned that the work in between starts is more important.

“Lifting, running especially, keeping up with my throwing program and my bullpens,” Ross said. “I think with every game that I go six, seven innings, each game is still building up arm strength so it gets easier to go farther and last longer before I get tired late in the game. Definitely the conditioning stuff and in between games is probably the most important.”

While he was limited each start in the minors recently, Ross isn’t in the majors. “I don’t think we have that luxury,” Williams said. “If he’s pitching well, he’s pitching well.” Ross believes his aggressiveness and the help of the defense has allowed him to pitch much deeper into starts in the majors than in the minors. He is averaging only 93 pitches per start despite going at least six innings in five of six. So although his innings may begin to reach uncharted territory, Ross has managed to be efficient.

“Everyday someone is making a good play behind me somewhere,” Ross said. “… All those things kinda blend together and help me go deeper into games. Hopefully I can keep it up.”

[Boswell: Nats’ winning formula is as easy, and difficult, as 1-2-3]

While in the majors, Ross said he is forcing himself to improve his change-up. He is throwing his signature Ross family slider 36 percent of the time, which would be fifth most in the majors if he qualified. His older brother, Tyson, throws his slider 46.5 percent of the time, by far the most in baseball. But some believe a slider can cause more strain on the arm. And, in order to continue developing and holding left-handers at bay, Joe Ross will need his change-up, too.

“In my mind it’s my third pitch and certain situations if I’m going to throw a pitch and I’m going to get beat, I want to get beat with my best pitch or my second best pitch,” Ross said. “It’s kinda comes down to trusting myself and trusting my change-up and knowing that it’s a good enough pitch to get outs and throwing it will help keep the batters off balance so they can’t just sit on two pitches.”