The way Addison Russell started out the 2014 season, it seemed that only an injury could slow him down on his march to the big leagues. Unfortunately, that's exactly what has happened.

The No. 1 prospect in the Oakland A's system, and ranked No. 12 overall on MLB.com's Top 100 prospects list, Russell was diagnosed with a Grade 3 right hamstring strain -- a tear of the upper hamstring that's expected to keep the shortstop out for at least a month, the club told MiLB.com on Wednesday.

Russell had a minor hamstring injury, also on his right leg, during Spring Training, but this injury is believed to be in a different part of the hamstring. The No. 5-ranked shortstop prospect came out of his Double-A game with the Midland RockHounds on Friday and hadn't played since. He was placed on the disabled list, retroactive to Saturday.

Russell -- the A's first-round pick, taken No. 11 overall in the 2012 Draft -- had homered in Friday's game, the second contest of the season. He had five hits in his first seven at-bats before the injury put him on the shelf, then he came out of the game when he felt what he thought was a cramp.

"It caught me off guard, so I told [RockHounds manager Aaron Nieckula] I didn't want to risk it," Russell told MiLB.com after the game. "He said, 'All right, I believe you' and took me out of the game. It's feeling good now. It's frustrating, but you've got to play it safe."

If Russell has no lingering issues upon his return, he's expected to continue his quick ascent up the A's organizational ladder. Oakland moved Russell aggressively, sending him straight to the Class A Advanced California League for his first full season in 2013. He was the league's youngest player at the start of the season and more than held his own, hitting .275/.377/.508 with Stockton and going to the All-Star Futures Game, all at the age of 19.

Russell played well in big league camp this spring, going 7-for-25 in 12 games. A's starting shortstop Jed Lowrie is a free agent after this season, and Russell could very well be the heir apparent.