Drew Storen is out for the season after an act of frustration left him with a broken thumb. (Toni L. Sandys/The Washington Post)

MIAMI — Yes, things could get worse for these Nationals. Right-hander Drew Storen broke his thumb Wednesday night and is likely lost for the season, according to Nationals Manager Matt Williams. After he allowed the go-ahead home run to Yoenis Cespedes in Wednesday night’s loss to the Mets, Storen shut the lockbox on his locker a little harder than he might have otherwise, powered by the frustration of that outing and his three-walk showing the night before. He has a non-displaced fracture in the tip of his right thumb. The Nationals have no sense of his timetable, though the injury will almost certainly end his season.

“I think it’s definitely unfortunate. He was pitching so well up until a couple weeks ago, then he struggled,” Nationals General Manager Mike Rizzo said. “I guess his frustration boiled over and sometimes you react and sometimes you react inappropriately. It makes it tough on his teammates. It hurts the team. We’ve gone through this a couple years ago with another relief pitcher, and it really affects the other bullpen members. It’s unfortunate. We’re not too happy about it. But Drew’s a competitor, and unfortunately he chose a route to let his frustration out that affects the ballclub.”

Storen did not punch his locker like Nationals reliever Ryan Mattheus did in 2013, but what he did was enough to leave his thumb swollen by the time he reported to Marlins Park Friday. He tried to throw, but “couldn’t really be effective doing it,” Williams said. Storen then reported the trouble. He flew back to D.C. Saturday, and will see a hand specialist in Baltimore.

“Regretful that it happened. A little bit embarrassed about it, of course,” said Williams, asked what feelings Storen expressed about the incident. “He’s a competitor. He was frustrated and he made a mistake.”

Storen’s fall from late-inning relief grace was swift, a plunge that closely coincided with his switch to the eighth-inning after the Nationals acquired Jonathan Papelbon at the trade deadline. Storen dominated first two outings as set-up man, striking out two batters in nine- and 10-pitch scoreless innings. He threw five straight scoreless eighths in late July and early August.

Then, he faltered. He allowed 13 earned runs in his last 13 2/3 innings, including a puzzling three-walk showing in the fateful seventh inning of Tuesday night’s loss, then that home run to Cespedes Wednesday. He is pitching to a 6.05 ERA in the eighth inning this year, and 1.62 ERA in the ninth. He has allowed three home runs in 19 1/3 innings of eighth-inning work. He allowed one in the ninth inning, that in a 16-1 game in Tampa Bay.

“It’s a game of adjustments and his role was adjusted,” Rizzo said. “Early on, the adjustment worked fine. He threw great I think the first five or six times that he was setting up for Jonathan. Since then, he was a guy who was a little bit inconsistent with his command and with his stuff, and really just kind of fell into a rut and he couldn’t get out of it. We trust his stuff. We know what he can do. Unfortunately his season has been sidetracked by kind of a needless injury.”

Storen may have pitched his last game as a National. He would not comment about the deal that brought Papelbon in and bumped him from his closer’s role, but he and his agent met with Rizzo afterward to discuss the situation. Storen is not a free agent until after the 2017 season, but the Nationals could opt to trade him this offseason.

Jokes about his recent struggles aside, Storen’s absence leaves the already hemorrhaging Nationals bullpen without its set-up man. Williams said the team “has options” such as veterans Casey Janssen and Matt Thornton, and less experienced options Blake Treinen and Felipe Rivero. Storen joins fellow right-handers Craig Stammen (flexor), David Carpenter (shoulder), and Aaron Barrett (Tommy John) as anticipated late-inning relief options lost for the season.