(Photo by Jonathan Newton / The Washington Post)

Reliever Ryan Mattheus was on his way to Houston on Monday evening to join the Nationals for their series against the Astros starting Tuesday, according to multiple people familiar with the situation.

Mattheus started the season at Class AAA Syracuse after he suffered a chest injury early in spring training and never recovered in time to begin the season at full stamina. In nine appearances at Syracuse, Mattheus has a 5.40 ERA with eight strikeouts, 11 hits and three walks over 10 innings. Regardless of his performance in April, Mattheus offers the most recent experience of any reliever at Syracuse.

It remained unclear which pitcher Mattheus would replace on the Nationals’ roster. Taylor Jordan has struggled with his velocity all season, especially Sunday as he battled a fever and a headache. Aaron Barrett was uncharacteristically wild Sunday, and the Nationals sent him to Class AAA once before, even though he has been mostly excellent in his rookie season.

Last year, Mattheus punched up a 6.37 ERA in 37 appearances. He missed several weeks after he broke his right, throwing hand punching a locker.