The Astros optioned Martinez, who leads the team with 54 RBIs, and infielder Matt Downs to the Minor Leagues following Thursday's loss to the Nationals. Both had options remaining and will likely be back up at some point in September when rosters expand.
Earlier in the day, the Astros acquired infielder Tyler Greene from the Cardinals in exchange for a player to be named or cash and will have him in uniform for Friday's series opener against the Brewers. The club will make another roster move to add a player before the game.
"I'm not going to look at it in a negative way," Martinez said. "I'm not going to go down there and try to be bitter. I'm going to use it as a growing experience."
Martinez admitted he's lost some confidence.
"I felt like I started off good and went through kind of a struggle and hit a plateau and never got hot again," he said. "The confidence was always there. It was never boosted back up again."
Martinez is barely a year removed from making his Major League debut, which came last August after Hunter Pence was traded to the Phillies. He was called up from Double-A Corpus Christi, so he will be making his first appearance on a Triple-A roster when he joins the RedHawks.
He went 0-for-4 with a strikeout on Thursday, dropping his batting average to .235 with 11 homers. Martinez, who leads the team with 87 strikeouts, had been hitting just .218 since April 22, including a 6-for-54 stretch April 22-May 13.
"He's in a situation where he's going through a little funk and because he has that option left, it's better if he got out of that funk the next couple of weeks in the Triple-A level instead of trying to work out of it here," manager Brad Mills said. "That's exactly what I told him, 'You're going to fight through this funk.'"
Martinez was disappointed in the move, but was focusing on positives.
"It's obviously tough," he said. "You never look forward to that, you never expect it. You have to take it positive and go down there and try to get my swing [right], the same swing that got me here, and I'm just going to keep moving forward and keep working hard to come back."
Martinez simply hadn't been squaring up balls like he did last season, when he burst onto the scene and hit .274 with six homers and 35 RBIs in 53 games in his Major League debut. He had 28 RBIs last August, which were the most for any Astros rookie in any month.
"You talk to hitters, and how hitters get hot is hit the ball on the barrel, and when you hit the ball on the barrel, you get that feel again," Martinez said. "I think that's the biggest thing I feel that I lost a bit. It's never easy up here in the first place with the guys pitching and having the stuff they have and you're battling. It's a little bit tougher to find that barrel, but it's the big leagues and that's why guys get paid a lot of money to play up here. It's not that easy."
Downs, meanwhile, was hitting .209 with seven homers and 13 RBIs in 154 at-bats, many of which had come off the bench. He was hitting .311 (14-for-45) in his last 21 games, but hadn't been able to gain the consistency he had last year, when he was arguably the best pinch-hitter in baseball.
When he wasn't starting, Downs found himself in the unenviable position of pinch-hitting late in games, often against the other team's closer.
"Here's a guy that's prepared so well for his role and done such a good job in facing some of the best pitchers he faces every night," Mills said. "In the last three innings is usually when he gets his at-bats, and that's tough. That's not an easy assignment. Last year, he was exceptional at it and this year he hasn't been quite as exceptional. But he's been professional about it how he prepares."