"It's just as much mentally as physically," Melvin said. "It's a grind playing shortstop every single day. He's been out there every single day. It just looked like maybe a little bit recently here it might be time for a day."
Semien acknowledged he's struggled recently, saying, "I think I played myself into a day off." Semien's hitting just .207 over his last 22 games and is hitless in his last eight at-bats, striking out four times.
He's also made five errors in eight games after committing eight in his first 88 games.
"I think sometimes mentally a little bit it gets away from you," Melvin said. "Whether or not your legs are 100-percent there. You're trying to maintain that pace, but in this game it's difficult to do."
Semien's made stark improvements in the field after committing 35 errors last year -- a product of those daily sessions with Washington. He's also second among Major League shortstops in home runs (20) despite moving around in Melvin's batting order, having hit in every spot except third and fourth.
His growth hasn't been lost on Melvin, especially defensively.
"It's been pretty remarkable," Melvin said. "I don't think I've ever seen a guy make those kind of strides defensively at the big league level from one year to the next."
Melvin said Thursday that Semien presumably wanted to play 162 games this season, but it wasn't likely to happen. Semien's dealt with a sore right shoulder prior to the All-Star Break, and said Thursday it's not an issue.
"There's been a lot of ups and downs mentally and physically this year," Semien said.
"I like to play through any type of little thing that hurts. I think there's a difference between things that hurt and being injured. Anything that hurts, I'm going to play through it. Mentally, you're going to have slumps. These past two games haven't been good. So I'll use this to get myself back right."
Mark Chiarelli is a reporter for MLB.com based in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.