Harper took to Twitter to share a post-surgery photo:
On the road to recovery..Everything went great and I'll be back soon! Thank you to all the fans for the support! pic.twitter.com/66Wn7sxHQ9
- Bryce Harper (@Bharper3407) April 29, 2014
Harper, 21, is expected to be out until at least early July, multiple sources told ESPN.com's Keith Law.
Manager Matt Williams would not commit to a time frame, but said "that time frame is out there" after reports Monday that he would be out until at least July.
"The doctor reported that everything went fine, and we got a little message from Bryce about getting back and taking BP post-surgery," Williams joked.
"It went fine, we'll have to see how long it takes ... we expect him to heal fast. Given his history, he has healed pretty fast. We are optimistic about it, but we're not really sure how long it is going to take."
The two-time All-Star was placed on the 15-day disabled list on Sunday with what was then called a sprained left thumb.
Williams talked about what Harper's absence will mean for his team.
"It hurts a lot. He's a fantastic player," Williams said. "We'll certainly miss him, but we're going to have to step up."
Harper was injured on Friday night against San Diego on a headfirst slide into third base on a triple. He remained in the game until after the next inning.
Despite the injury, Williams is not opposed to headfirst slides.
"Bryce had another collision sliding feet first earlier in the year, and he hurt himself last year sliding feet first," Williams said.
"It's something that you can't control. The play that he hurt himself on, he was trying to get to third base the quickest he could, and I don't know if he is safe if he slides feet first. He was safe sliding head first, but he got the thumb in the wrong position."
Harper is batting .289 with one home run and nine RBIs this season.
Harper was the National League Rookie of the Year in 2012 after hitting .270 with 22 homers and 59 RBIs.
The extended loss of Harper is a significant blow to a Nationals roster already riddled with injuries to key players, among them catcher Wilson Ramos, third baseman Ryan Zimmerman (both with hand injuries) and starting pitcher Doug Fister (back).
Harper missed 44 games last season, his second in the majors, with a left knee injury. He was injured in mid-May when he slammed into the right-field wall at Dodger Stadium.
Information from ESPN.com's Keith Law and The Associated Press was used in this report.