Washington Nationals manager Davey Johnson says star pitcher Stephen Strasburg might have has irritated a nerve in his right arm using an electrical stimulation machine.

The machines are used by athletes to build strength and are attached with adhesive electrodes. Johnson said Tuesday the device could have been placed too close to a nerve in Strasburg’s right arm.

Johnson says it is too early to determine whether Strasburg will make his next scheduled start on Saturday at Pittsburgh. The manager wants to see how the right-hander throws in a bullpen session.

Strasburg frequently shook his right arm while pitching six innings and allowing two runs in the Nationals’ 3-2 loss to Atlanta on Monday night.

Marlins’ top hitter out a month

Miami Marlins slugger Giancarlo Stanton expects to be sidelined for about a month because of a strained right hamstring.

Stanton underwent an MRI on Tuesday and said the diagnosis was a grade-two strain on the one-to-three scale for the injury. He was hurt trying to beat out a grounder in Monday’s 15-inning victory over the New York Mets, and was put on the 15-day disabled list Wednesday.

The injury occurred just as last year’s NL slugging leader showed signs of emerging from a prolonged slump at the season’s start. He hit his first home run Saturday, and two more homers Sunday.

Now the Marlins, already saddled with the worst record in the majors, will be without their best hitter for several weeks.

Red Sox activate Hanrahan

Reliever Joel Hanrahan was activated from the 15-day disabled list by the Boston Red Sox after two weeks out due to a sore right hamstring.

The move Tuesday fills the roster spot that opened when right-hander Daniel Bard was optioned to Double-A Portland following Sunday’s win over Houston.

Hanrahan hurt the hamstring April 3 against the New York Yankees in his second appearance of the season. Hanrahan will serve as setup man to right-hander Andrew Bailey, who has saved five games in six chances since Hanrahan went on the DL. Bailey is 1-0 with a 1.46 ERA in 13 games.

Around the leagues

The New York Yankees placed Kevin Youkilis on the disabled list. The Yankees said that Youkilis has a lumbar spine sprain. Infielder Corban Joseph was recalled from Triple-A Scranton/Wilkes-Barre. … The Pittsburgh Pirates designated left-hander Jonathan Sanchez for assignment and called up right-hander Bryan Morris from Triple-A Indianapolis. … Outfielder Delmon Young was activated from the 15-day disabled list by the Philadelphia Phillies after missing the first 26 games because of offseason surgery on his right ankle. … The Atlanta Braves placed right-hander Luis Ayala on the 15-day disabled list due to an anxiety disorder and recalled right-hander David Carpenter from Triple-A Gwinnett. … The Tampa Bay Rays activated designated hitter Luke Scott from the disabled list and designated Shelley Duncan for assignment.