"The toughest thing was Westbrook," Cardinals manager Tony La Russa said. "He's our protection during the series if the starter has an early problem or we go extra innings, and in that role, to be available every day, you can't stay in shape."
McClellan moved from a starter to reliever this season. Even though he's right-handed, McClellan is strong against lefties, allowing just a .206 average.
Lynn had been out since early August because of a strained left oblique, but had a 2.22 ERA over 16 relief appearances.
Westbrook was the only Cardinals player who didn't appear during their first-round series against Philadelphia and went 1-3 with a 4.13 ERA against the Brewers this year.
Schumaker is out with an injury after straining his right oblique in the Cardinals' 1-0 win in Game 5. If the Cardinals need an additional outfielder, La Russa said second baseman Nick Punto could make the switch. Punto has 11 outfield appearances in his career.
The Brewers did not make any changes to their roster from the NLDS.