Ramirez, who has missed the last three games due to swelling in his right hand, took swings for about 10 minutes shortly after 3 p.m. ET. He also fielded grounders at third during pregame warmups.
"The best I've seen him swing in a little while," Guillen said. "I think he has a little better idea about his swing, and I think he's happy with what he sees. So far, things have gone [Monday] the way we thought. He's playing [Tuesday]."
Ramirez was hospitalized in Pittsburgh on Friday, when his right hand became infected. The third baseman previously injured the hand in St. Louis on July 8, when he hit a cooling fan in the visitors' dugout at Busch Stadium out of frustration. The incident caused Ramirez to get two stitches in the knuckle of his ring finger.
The infection occurred when Ramirez failed to take antibiotics prescribed to him after the incident, and the swelling in his hand kept him out of the lineup in Pittsburgh. During the weekend, Ramirez said the inflammation prevented him from being able to grip a bat or a baseball.
Guillen initially expected Ramirez to miss a few more games, but the swelling was down considerably Monday, and the manager said the third baseman was available to pinch-hit.
"He got the go-ahead from doctors," Guillen said. "It's better. He's swinging the bat good. If we can pinch-hit him [Monday] or something, I think he's available to do it."
With lefty Mike Minor starting for Atlanta on Monday, Donovan Solano got his third start at third base this season, and his first since June 15 against the Rays. The right-handed hitter has been effective against left-handed pitchers in limited opportunities, hitting .333 with two doubles, a triple and four RBIs.
"Every time we play this kid, he's been great," Guillen said. "He does a lot of great stuff for us in any place -- outfield, pinch-hit, pinch-running, every time we send him in. It's a pleasure to see him play."