"I hope it's just two weeks," said manager Jim Riggleman, after reviewing Wednesday morning's MRI results with his leadoff man and the club's medical staff.
Washington also announced transferring pitcher J.D. Martin (bulging disk in back) to the 60-day DL, presumably to open a 40-man roster spot for the player who will fill Morgan's cleats.
Riggleman said that player would be "a bat off the bench" and wouldn't specify if an outfielder or infielder would receive the call-up. He all but ruled out promoting a third catcher -- Triple-A Syracuse's hot-hitting Wilson Ramos.
Morgan, who has felt lingering tightness his hip flexor since attempting to track down a fly ball in a July 21 game against the Reds, said after Thursday's defeat that he "feels like he can play," and that he didn't understand why he was being deactivated.
Morgan will stay with the club during its trip this weekend to Los Angeles, but, while his presence can only aid his teammates, the Nats' outfield didn't miss a beat without him in the final two games of its series in Arizona.
Roger Bernadina, who will bat leadoff and man center field during Morgan's hiatus, went 4-for-8 with a home run and a stolen base in his stead. Willie Harris will back up Bernadina in center.
In addition, Mike Morse, who has shifted into Bernadina's right-field spot, went 2-for-3 and smacked his seventh home run on Wednesday before an 0-for-4 day at the plate on Thursday.
"Having good at-bats, seeing the ball, working deep in the count -- usually when I find myself doing that, I have good results," said Morse, who is batting .324 (25-for-77) when he starts this season. "We got some good outfielders on the bench and playing. Until [Morgan] comes back, I'll do whatever I can."