The Reds' Minor League Hitter of the Year and a Florida State League All-Star last season, Rosales had been invited to camp despite having only three years of professional experience. He was a 12th-round pick in the 2005 First-Year Player Draft.
Rosales, 24, impressed Reds manager Dusty Baker this spring, batting .321 (9-for-28) with a home run, two RBIs and six runs scored.
"He had a real good spring," Baker said. "Played all over, hustled, showed great attitude, great aptitude. For a young guy, he can play different positions hard. He can play both sides of second base, works hard, hustles all the time."
On Saturday, the Reds optioned catcher Craig Tatum and right-handed pitcher Daryl Thompson to Double-A Chattanooga. The club also re-assigned right-hander Jon Adkins to the Minor League camp.
The cuts left Cincinnati with 50 players on the roster, including pitcher Bobby Livingston, but Livingston is on the 60-day disabled list.
Further cuts will be coming soon, as the Reds still have 25 pitchers in camp with Opening Day just two weeks from Monday.
"These innings are becoming more and more precious," Baker said.
Jim Molony is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.