While Washington back-dated the 15-day allotment in case he's ready in a couple of weeks, there is concern within the organization he could miss several weeks.
That's consistent with what unnamed Nats source told the Washington Post. "Doesn't look good," that source told Nats beat writer Adam Kilgore.
Harper is scheduled to see a hand specialist Monday, so there's still some uncertainty until that exam. The Post story mentioned Josh Hamilton's six-to-eight-week stay because of ligament damage in his thumb as possibly comparable.
Like Hamilton, Harper injured his thumb on a head-first slide. His injury occurred Friday night.
Nats manager Matt Williams told Nats writers the X-rays were "negative." But that doesn't mean the news will be all positive.
Harper, 21, was limited to 118 games last year because of side, knee and hip injuries.
Harper is known for his aggressive play and hustle, though Williams sat him a game for not running full speed on a grounder back to the pitcher a few days earlier. At the time Harper was concerned about a mild leg injury.
Nate McLouth is likely to be Harper's main replacement.