Milton was to be reassessed today by Reds medical director Dr. Timothy Kremchek to determine the significance of the injury.
"Hopefully, it's nothing serious and he won't miss a start," said Reds manager Jerry Narron.
Milton went 0-1 with a 6.59 ERA in four starts this spring, allowing 23 hits, including three home runs, in 13 2/3 innings.
Kyle Lohse started on Saturday in place of Milton.
Narron also expected right-hander Victor Santos, left-hander Jon Coutlangus and righty Todd Coffey to get some innings against Florida.
Milton went 8-8 last season with a 5.19 ERA in 26 starts. His season was interrupted by surgeries on his left elbow and left knee.
Valentin's vote: Javier Valentin will likely be one of three catchers on the Reds' Opening Day roster, along with starter David Ross and recently acquired backstop Chad Moeller.
Valentin, who also plays first base and was the club's top pinch-hitter last season, said he's unsure of his exact role, but he'll do whatever is best for the team.
"If they're going to bring three catchers, it's fine with me," Valentin said. "I know what I can do. It's a manager's decision. There are only 25 guys that can make the team. It's a tough decision. I had a good year last year. I'll be ready for whatever situation."
Valentin led Reds pinch-hitters in hits (12), home runs (4) and RBIs (12) last season.
Reckless Ryan: With just his second career Opening Day start likely in less than 48 hours, Ryan Freel is pulling in the reins on his reckless abandon -- for one day.
"I don't want to do anything stupid," Freel said. "I'm really good at doing that."
"My ribs are still sore," he said. "I ran all that way to catch that ball. It's not that I do those things for show. I have a lot of fun doing it."
Unlike in past years, Freel did not play a position other than the outfield during Spring Training. He is expected to start in center field on Opening Day against the Cubs.
"I'm a little nervous," Freel said. "Opening Day in Cincinnati is an amazing thing. To see the fans get so psyched up puts a little more pressure on you. You want to perform well. It doesn't help that I'm so intense anyway."
It's a gem: Dayton was nicknamed the "Gem City" more than a century ago, and it's proved to be a gem for the Reds organization since the Dragons became their Class A affiliate in 2000.
Saturday's exhibition game marks the first time the Reds have played a game in Dayton.
"It's our way of paying back the people of Dayton," said Narron. "[Fifth Third Field] is a beautiful ballpark. Our organization raves about it and what [the Dragons have] done for the Reds over the years. The guys that played here just flat out loved it."
Fifth Third Field, with an official capacity of 7,230, has been sold out for seven consecutive seasons. The Dragons finished with the seventh-highest attendance in Minor League Baseball last year.
Louisville looking Sweet: Louisville Bats manager Rick Sweet didn't hesitate to point out his club will have good pitching.
Bobby Livingston, who challenged Matt Belisle and Kirk Saarloos for the Reds' fifth-starter job, will be at the top of Sweet's rotation.
Homer Bailey, Cincinnati's first choice in the 2004 First-Year Player Draft, will be in the rotation along with Mike Gosling and Phil Dumatrait. The fifth starter at Louisville, like the Reds, is still undetermined.
"The Reds have another move to make," Sweet said. "If they trade a pitcher or two, then Tom Shearn will start."
Shearn is a graduate of Briggs High School in Columbus, Ohio.
"We are going to be solid defensively," Sweet said. "We will be strong up the middle. We have three outfielders who can play center field."
Bubba Crosby, Jay Bruce, the Reds' first draft choice in 2005, and Tyrell Godwin are the trio.
Votto defensive: Joey Votto has proven that he can hit in his five seasons with the Reds organization. He is counting on defense to get him to the next level.
"The last thing Jerry Narron told me was that if I don't work twice as hard on my defense as I do my hitting, he's going to whack me," Votto said before taking his position at first base in an exhibition game in Dunedin, Fla., against the Blue Jays on Saturday.
The 23-year old, a second-round choice in the 2002 First-Year Player Draft, took the instruction with a big smile.
"I've always worked pretty hard," Votto said. "But I'm learning to focus on every play, and that is hard to do for 230 days."
Boone visits: Former Reds third baseman Aaron Boone, who signed a one-year contract with the Marlins in December, stopped by the Reds clubhouse at Fifth Third Field on Saturday.
Boone played seven seasons in Cincinnati.
Coming up: The Reds will work out on Sunday afternoon at Great American Ball Park in preparation for Monday's Opening Day game against the Chicago Cubs at 2:10 p.m. ET. Aaron Harang will start against Carlos Zambrano.
Jeff Wallner is a contributor to MLB.com. Gary Schatz also contributed to this report from Dunedin, Fla. This story was not subject to the approval of Major League Baseball or its clubs.