"I've got one but it's not broken in," Hernandez said.
A short time later, the Reds got the news that second baseman Brandon Phillips also had the flu and needed to be scratched.
Until Wednesday, Votto had been the only Cincinnati player to log every inning of every game. During the 15-3 blowout loss to the Brewers, he was lifted in the sixth inning for Rosales. When Rosales moved to third base in the ninth inning, Hernandez played first base for just the eighth time in his career.
"When you get to play another position, it's fun," Hernandez said. "I'm here. If they want me to be the bat boy, I will be the bat boy. I'm ready to do whatever the manager asks me."
Votto's .378 average this season is second best in the National League. He has three home runs, 23 RBIs and a .466 on-base percentage.
Rosales, who was a shortstop and third baseman as he came through the Reds' farm system, played 106 games at first base during 2007 in the Minors as he recovered from an elbow injury. He played 19 games at first base last season with Triple-A Louisville.
If called upon to replace Votto again, Rosales pronounced himself ready.
"I know I have a lot of work defensively to do," said Rosales, who started at third base on Thursday. "It's tough shoes to fill. I would get the job done and do our best to keep our defense going."
After Votto and Phillips were scratched, Jerry Hairston Jr. was moved from shortstop to second base. Paul Janish was inserted in the lineup at shortstop.
Speaking after Thursday's game, Reds manager Dusty Baker did not know if Votto and Phillips would be able to return to the lineup on Friday.
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.