Doug Fister. (Photo by John McDonnell/The Washington Post) Doug Fister. (Photo by John McDonnell/The Washington Post)

Doug Fister threw his first bullpen session on Friday following nearly two weeks of rest for his inflamed elbow, and on Saturday morning his arm felt good, according to Manager Matt Williams. The manager said he spoke with Fister on Saturday morning and was pleased to hear he felt good.

The next step in Fister’s timetable, however, is unclear. Depending on how he feels following treatment on Saturday and Sunday, he could pitch in a minor league game as soon as Sunday.

The Nationals will not require a fifth starter until April 6, so they have ample time to get Fister innings before then. Williams is targeting March 19 as a day to begin ordering the starting rotation in the regular season order.

>>> Ryan Zimmerman is back in the lineup on Saturday after sitting out of games for four days because of soreness in his shoulder, which was surgically repaired before the 2013 season. Zimmerman participated in workouts on Friday, taking grounders and throwing across the diamond, and feels better, Williams said. Zimmerman will be back in the field at third base in a game on Sunday pending any residual soreness.

“We’re progressing him slow but we need to get him ABs to make sure,” Williams said. He said he believes Zimmerman’s shoulder is experiencing regular soreness for this point of spring training, and because the infielder’s workload has increased with drills at first base.

Williams said it isn’t clear yet when Zimmerman will make his debut at first base this spring. Because of the rest, Williams is primarily concerned with getting Zimmerman the needed work at third base. If Zimmerman doesn’t play first base in the spring, Williams said he believes he could still handle playing there during the regular season.

“He’s done enough work so far that even if it was the regular season that he’ll be fine,” he said. “We’ll see if we can do that a few times in the next 10 days. … But we have to monitor him. I want him to play third first, no pun intended, and first second.”

Ideally Zimmerman would play first base, a new position for him, during the spring in a low pressure environment before he does so in the regular season. Williams said he could send Zimmerman to get work at first in a minor league game if needed.

>>> Ian Desmond will return to the lineup on Sunday after resting the previous three days with a chest cold and cut on a finger on his throwing hand, Williams said. Bryce Harper is playing Saturday despite still feeling the lingering effects of a cold.

>>> Ryan Mattheus (chest) and Ross Ohlendorf (back) are expected to return to games later this week after extended time away dealing with injuries, Williams said. That, however, would leave each pitcher with about a week or so to build up enough innings. Both players are competing for a spot in the Nationals bullpen, but now it is increasingly slim that either will be with the team when the team breaks camp.

Williams, however, wouldn’t rule out the possibility that either could still earn a spot.

Mattheus “is certainly behind the eight ball in that regard and needs to build himself up,” Williams said. “That doesn’t mean he’s not going to break with us. But we have to evaluate that.”

If neither is ready, Tanner Roark could have a clearer path to make the team. Roark is competing for the fifth spot in the rotation, but has experienced as both a long reliever and starter in his minor league career, and did both well during his stint in the majors last season.

“His versatility in the pitching staff helps,” Williams said. “He can start he can relieve, he can start. That’s nothing but a positive for him to break with the club.”