WASHINGTON -- Struggling Nationals reliever Trevor Rosenthal has agreed to go to extended spring training in West Palm Beach, Florida.

The 28-year-old right-hander was placed on the 10-day injured list on April 26 with a viral infection. Rosenthal (0-1) has appeared in seven games with Washington, pitching to a 36.00 ERA. He did not record an out until his fifth appearance.

"There's no timetable," Nationals manager Dave Martinez said Monday. "We just have to get him built up again."

Rosenthal -- an All-Star in 2015 with St. Louis -- underwent Tommy John surgery in 2017 and missed all of last season.

"Health-wise, everything feels good, just ironing out some timing and getting just really the reps in to let my body figure it out," Rosenthal said.

Signed in the offseason as a potential setup man for closer Sean Doolittle, Rosenthal has walked nine of the 28 batters he has faced and has thrown five wild pitches.

Washington entered Monday with the second-worst bullpen ERA in the majors at 6.57, ahead of only Baltimore.