WASHINGTON -- The Nationals are expected to call up right-hander Marco Estrada on Tuesday from Triple-A Columbus. It's not known which player will be sent down to the Minor Leagues.

Estrada was a combined 9-6 with a 3.09 ERA in 25 starts for Columbus and Double-A Harrisburg.

However, Estrada, who was selected in the sixth round of the 2005 First-Year Player Draft, will work out of the bullpen, replacing Luis Ayala, who was traded to the Mets on Sunday morning.