Baker is owed $4 million in 2010, the final year of his contract.
The fifth-place Reds are 46-61 and 11 1/2 games out in the National League Central and just one game above the last-place Pirates. Before Wednesday's victory, Cincinnati had lost a season-high eight in a row and 14 out of 15 games.
The Reds' roster has been ransacked with numerous injuries, which accelerated the slide since mid-July. Key players sucha as Jay Bruce and Ramon Hernandez are currently on the disabled list and front-line starting pitcher Edinson Volquez is out for the season.
"They've been part of it, but things have not gone our way," said Castellini of the injuries.
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.