WASHINGTON -- The Nationals will call up reliever Fernando Rodney ahead of Tuesday’s series opener in Miami, a source confirmed to MLB.com on Monday.

Rodney started the season with the A’s, but he was released in May after giving up 15 earned runs on 20 hits in 14 1/3 innings (9.42 ERA) with 14 strikeouts and 12 walks. He had been pitching at Triple-A Fresno for the past month and given up five runs (four earned) in eight innings (4.50 ERA) with 11 strikeouts and nine walks. Once the move becomes official, Rodney, 42, will become the oldest active pitcher in the Majors.

Rodney has been an effective Major League reliever as recently as last year, however, when he made 68 appearances between the Twins and A’s combined and posted a 3.36 ERA, which was good for a 127 ERA+. He even made Oakland’s postseason roster and made an appearance in their loss in the American League Wild Card Game against the Yankees.

The move, which was first reported by the Washington Post, was made possible when the Nationals cleared a 40-man spot on Sunday be releasing reliever Trevor Rosenthal, who’s perplexing struggles were the genesis of their bullpen woes.

Rodney will become the latest veteran reliever Washington will try out in its bullpen. This season alone, the Nationals have acquired Dan Jennings, Javy Guerra, Jonny Venters, who remains in the Minors, and now Rodney to help aid a bullpen with a 6.29 ERA, which entered play Monday as the highest in the National League.

Washington had a free spot open on it’s 25-man roster because the team announced earlier Monday that starter Erick Fedde has been optioned to Fresno. Fedde’s demotion comes as a bit of a surprise, considering he had been filling in as the team’s fifth starter after Jeremy Hellickson landed on the injured list last month. But Fedde has struggled recently, posting a 5.49 ERA with 10 strikeouts and 11 walks over his last four starts as he struggled to pitch deep into games.

After Austin Voth’s performance during his spot start in Sunday’s series finale, Washington was comfortable optioning Fedde to the Minors, making room for Voth to join the rotation. Voth struck out a career-high seven batters and held the Braves to four hits in six innings, yielding a pair of home runs to Ronald Acuña Jr. and Josh Donaldson. On Sunday, Voth’s fastball averaged 93.9 mph, an increase from the 91.3 mph average velocity he averaged during his stint in the Majors in 2018, when he made four appearances and two starts.

That spike was consistent with the reports that the Nationals received on him in the Minors, and Voth also credited the nine days off in between starts as a reason his arm felt so lively.

“I really liked what I saw. I really did,” Washington manager Dave Martinez said. “Everything was good. We'll see where he fits in, but I was very impressed. Especially in the sixth inning, still throwing 94 miles an hour. And [he] looked very poised. It was awesome.”