WASHINGTON -- The Nationals placed struggling reliever Trevor Rosenthal on the injured list Friday with a viral infection, an issue the team revealed he had been battling during their recent six-game road trip in Miami and Colorado. Reliever Justin Miller has been reinstated from the injured list to take his spot on the roster.

Rosenthal had also been experiencing some muscle fatigue and dropped about 10 pounds in five days. He felt good enough to try and pitch in Wednesday’s series finale, but he gave up three runs and uncorked three wild pitches in one inning in a 9-5 loss to the Rockies where manager Dave Martinez said he “didn’t look right.” He was diagnosed by a Nats team doctor prior to Friday’s game against the Padres.

“He’s a big part of this team,” general manager Mike Rizzo said. “We need to get him fixed. And we need to make sure he’s healthy, fixed and getting his work in, whether it be here or the Minor Leagues.”

The Nationals have been searching for a solution to Rosenthal for weeks now, considering he has not been himself all year in his return from Tommy John surgery that forced him to miss the entire 2018 season. Each of his seven appearances this season have been, to some degree, a nightmare. He has completed just three innings, but allowed 12 runs with nine walks and three strikeouts, hitting three batters and misfiring with five wild pitches. Rosenthal owns a 36.00 ERA in seven games.

Among the solutions the Nats have discussed include sending Rosenthal to the Minors to iron out his issues, which Rizzo acknowledged Friday. Rosenthal would have to accept any demotion to the Minors as a seven-year MLB veteran, but Rizzo said Rosenthal has been open to any potential solutions.

“There’s nobody that feels worse about how he is performing than Trevor Rosenthal,” Rizzo said. “He’s a great teammate, the makeup is terrific; he wants to help his team, and he is going to do what he has to do to get better and to help the club.”

Prior to the game Friday, Rosenthal played catch in the outfield under the watch of the team’s training staff. Washington wants him to focus on regaining his strength during his time on the injured list, but the team also sees this as a chance to focus on the mechanical adjustments he’s struggled with for weeks.

“For right now, the main thing is get him healthy,” Martinez said. “Get his weight back, get him strong again, and then after that, it’s just kind of hone in on his mechanics. Really hone in on his mechanics. ... He’s going to be back, but we want him to be able to go out there and not worry about struggling. Just worry about throwing strikes and helping us win.”

Youth movement

The Nationals had three players under the age of 22 in the starting lineup Friday night with center fielder Victor Robles, left fielder Juan Soto and the club's No. 1 prospect per MLB Pipeline, shortstop Carter Kieboom, all playing together. It’s the first instance since 1997 of a team fielding a lineup with three position players under the age of 22, when the Marlins started Mark Kotsay, Edgar Renteria and Luis Castillo on July 27, 1997, according to Elias.

“This is the golden days of young players, man,” Rizzo said. “It seems like a lot of players that are very young and extremely talented in the league, and every team has a few of them. And we’re fortunate that we’ve got ourselves a handful of guys that are impact players at a very, very young age.”