Tanner Roark may get the call for Sunday’s start. (Alex Brandon /AP)

Following Tuesday’s game, Nationals Manager Davey Johnson said he would determine in a day whether Ross Ohlendorf would make his next start Sunday or if rookie Tanner Roark would get the call. Although he didn’t want to commit to a decision Wednesday, Johnson said Roark is still a possibility to start on Sunday night against the New York Mets.

Johnson said he wanted to hold off on a final choice until both players’ bullpen sessions after Thursday, just in case either had any issues. “I would like to give [Roark] an opportunity to start,” he said.

Roark, a 26-year-old right-hander, has impressed since his call-up earlier this month. In the minors, he was both a long reliever and starter. With the Nationals, he has been a long reliever and compiled a 1.04 ERA over 17 1/3 innings with 14 strikeouts and only four walks. As part of their evaluation of younger players over the final five weeks of the season, the Nationals also want to see how Roark performs as a starter.

Johnson had also expressed concern with Ohlendorf following his start on Tuesday night. Ohlendorf allowed only one run on three hits over five innings, and has a 2.49 ERA overall. The Nationals have won all four of his starts. But in the sixth inning, Ohlendorf’s fastball velocity dropped to 81, 83 and 85 miles per hour and Christian Yelich smashed an 85-mph fastball for a homer.

In the previous frames, the right-hander’s fastball was humming between 90 and 93 mph, even hitting 95 in the first inning. Johnson fears Ohlendorf was tiring too quickly, as he feels the right-hander has in previous starts. Ohlendorf said the drop in velocity was purposeful, saying they were “batting practice pitches”to throw off batters’ timing and he wasn’t tiring. Johnson still isn’t convinced.

“I love pitchers that add and subtract with their fastballs,” Johnson said before Wednesday’s game. “You generally subtract away and add in. You don’t subtract from your fastball and throw it in. That’s not a good idea. A BP fastball thrown inside is not a good idea.

“I know he went to Princeton but that ain’t a good idea – at any point in time in the count. When I came out, Willy said that was a four-seamer. I thought it was a change-up. He does add and subtract. He really ran out of gas the time, the sixth inning here before. I was ready for it this time. … It’s kinda scary when you’re getting ready to go through the meat of the lineup.”

>>> Johnson provided more clarity on Ross Detwiler’s status. Johnson said he spoke with head athletic trainer Lee Kuntz about the rehabbing left-handed starter. Johnson doubts Detwiler will return this season given how much time he has missed. Detwiler, who has been out with a herniated disk in his lower back since July 4, hasn’t yet thrown off the mound yet but believes there is enough of a window for him to return this year. He would have to go through a spring training-like throwing program with only a month left in the season.

Johnson fears Detwiler’s back may have been hurt during the World Baseball Classic but didn’t affect his performance until after his first five or six starts into the season when his numbers started to rise. Detwiler missed time in May and June with an oblique strain.

Johnson would like to see Detwiler pitch again this season but doesn’t believe there’s enough time. He wants to ensure Detwiler is completely past the injury before he gets back on the mound. He suggested Detwiler may need to play winter league baseball in Venezuela or the Dominican Republic. Detwiler has thrown only 71 1/3 innings this season.

“He probably feels pretty good but is this something that’s going go re-occur when he gets into the regular rotation and has four or five starts,” Johnson said. “He’s only going to have 70 innings. I think he needs to have, if he’s in the rotation, if he has a chance to throw 200 innings, he needs to have more innings now. So maybe winter ball or something. We gotta crank that thing up. If the rest cured the symptoms of the injury, but the injury is still there, we need to know. If there’s a little bulge in there that’s pinching a nerve, we need to fix it rather than rest and come to spring training and early in the season, boom, he’s down.”