The defenseman was injured in the second period of a 4-1 win in Game 4 on Friday. Boston leads the best-of-7 series.
Miller left with 12:33 remaining in the period after a hit from Capitals defenseman Dmitry Orlov.
Miller had passed the puck after carrying it into the offensive zone and was hit by Orlov above and between the face-off circles. He was tended to on the ice by the Boston trainer and skated off with some assistance.
"Kevan is back home, spent the night at the hospital," Bruins coach Bruce Cassidy said Saturday. "Went through a number of tests. Feeling better. That's what we've got."
RELATED: [Complete Bruins vs. Capitals series coverage]
Orlov was first assessed a major penalty, but it was downgraded after video review. He received a minor penalty for roughing Miller and one for roughing Boston forward Charlie Coyle after the play.
"[The official] told me, skating by, that he felt that when they reviewed it they made contact first to his shoulder, I guess, or whatever he said, upper body at the time, I forget," Cassidy said after the game. "But it didn't look that way from our vantage point."
Forward Brad Marchand gave the Bruins a 1-0 lead 33 seconds into the power play, at 8:00.
"Obviously huge," said Boston forward David Pastrnak, who had an assist on that goal. "'Millsy,' especially a guy like Millsy that steps up for every single guy in the room. We felt like we had to get it done for him. He's a big part of our team. That was our main focus going into the third, to get it done for him. At least get the momentum on the power play in the third and we got a huge goal there (at 29 seconds for a 2-1 lead). Our killers did an outstanding job. It was a huge response, stepping up for Millsy."
Boston killed six of seven penalties. Defensemen Charlie McAvoy played 8:49 shorthanded, Brandon Carlo played 7:02 and Connor Clifton played 6:23.
Miller had one assist playing 19:13 per game in the first three games of the series. He missed time in Game 2 on Monday after he was cut making a hit.
He was limited to 28 games during the regular season by a knee injury (Feb.19-April 6), and then missed games after he returned because of rest and a reported foot infection.
With Miller out in Game 5 (7 p.m. ET; USA, SN1, TVAS2, NBCSWA, NESN), the Bruins will move Clifton back to his natural right side, paired with either Jarred Tinordi or Urho Vaakanainen. Tinordi played 14 games for the Bruins during the regular season after being claimed off waivers from the Nashville Predators on Feb. 27. Vaakanainen had two assists in nine games this season but has never played in the NHL playoffs.
"[Miller's] a huge part of our team, he sticks up for everyone. So we wanted to do that for him and making sure that we're doing it the right way," Boston defenseman Matt Grzelcyk said. "We're beating them on the scoreboard and not taking stupid penalties. … We responded when we needed to, we played the right way for most of the game, and it was a great effort."
NHL.com staff writer Amalie Benjamin contributed to this report
