Mr. Bush also has aching knees that he attributes to age, said spokesman Scott McClellan.
The president, who turns 57 on July 6, initially ignored the pain that began in late April and "tried to run through" it, McClellan said. When the pain continued, he decided to quit running for a while.
The injury won't require surgery, and the running pause is not expected to be permanent. Just last week, Mr. Bush went for a slow run as he gradually tries to work back to his old regimen, McClellan said.
"This is something that's a runner's injury, something that an athlete will suffer from time to time," the spokesman said. "This is something that will just take time to heal."
Mr. Bush winked, smiled and nodded Friday as if to signal he is fine when asked about his recovery during an Oval Office appearance with Brazil's president. He alluded to the problems a day earlier by playfully clutching his left knee and grinning as he approached Air Force One for a trip to Minnesota.
An avid fitness buff, Mr. Bush hasn't let up on his daily exercise routine and has been cross-training, swimming and lifting weights to get in regular workouts, McClellan said.
Mr. Bush has been a runner for about three decades, and credits exercise with helping him quit drinking more than 15 years ago. Famously competitive, he pays close attention to his times and prefers fast, 3-mile runs to slower, longer jogs.