Martinez, considered one of baseball's top prospects from 2006-10, was claimed off waivers by the Astros in January. He was batting .319 with eight homers and 38 RBIs in 51 games at Oklahoma City, with a .374 on-base percentage and a .532 slugging percentage. Like Buck, he's a left-handed hitter.
Martinez's career has been marred by several knee injuries, but he's been healthy so far this season.
"We've got a guy who's hitting and has been swinging the bat real well," Mills said. "He's a young kid with a lot of ability, and I think we all know the history of his tools and we're hoping that now it's time for those tools to kind of blossom a little bit."
Martinez, 23, spent the majority of the 2011 season at Triple-A Buffalo, but did have a brief stint with the Mets. In 63 games with Buffalo, he hit .260 with eight home runs and 30 RBIs. He hit .227 in 11 games for the Mets with a home run, which came May 13, 2011, at Minute Maid Park off Astros pitcher Bud Norris.
Martinez also had brief stints with the Mets during the 2009 and 2010 seasons, appearing in a combined 36 games in that span. He has a .274 career average in six Minor League seasons after being signed by the Mets as an amateur free agent in 2005 at 16 years old.
"If they give me the opportunity to play every day, I'll try not to do too much and do the best I can and help the team," he said. "I want to swing the same I was swinging over there in Oklahoma."
What the arrival of Martinez means for starting right fielder Brian Bogusevic remains to be seen. Bogusevic has struggled this year, hitting .221 with two homers and 12 RBIs in 149 at-bats. Martinez got the start Saturday against a right-handed pitcher.
"I think [Martinez] is going to get more time than Bogey, maybe in the short term until we see what happens," Mills said. "Bogey's been pretty much our starting right-fielder against right-handed pitchers, and we're going to be facing a lot of right-handers. That's not taking away from Bogey, but at the same time we brought this guy up because he's hot, he's swinging the bat and we need to see him a little bit.
"I love Bogey and what he brings to the table. He brings a lot to the table. I'll sit down and visit with him and chat with him a little as we move forward."
Buck has hit .216 in 33 games with the Astros and hasn't been available to play because of a painful right heel that has him in a protective boot. He described his injury as tendinitis in the back of his heel, but said the tendon was sound.
"I can't remember doing something that caused it," he said. "Throughout [the second game of Monday's doubleheader] it started to get more and more tender, and after the game I couldn't really walk on it. Tuesday I couldn't walk at all. It's something we tried to get around and get some treatment and it has started to feel a little bit better."
Buck leads the Majors with a .538 (7-for-13) batting average as a pinch-hitter, but was hitting just .148 (9-for-61) as a starter. He didn't want to go onto the disabled list, but understands the club's decision.
"I probably could have talked them out of it if it wasn't for Carlos," he said. "He's a big part of our team and we're hoping he doesn't need to go onto [the DL]. You couldn't have two guys that were unavailable. It could be a blessing in disguise to allow me to get healthy and then get back on the field and contribute."