Farrell said he is not sure how many games Ortiz will start at the position.
Ortiz played most of his games this season as the team's designated hitter, and the Red Sox can't afford to have his bat out of the lineup when the series heads to the National League ballpark.
Ortiz is hitting .200 with three home runs and eight RBI this postseason.
The World Series starts Wednesday at Boston's Fenway Park. Games 3, 4, and 5 (if necessary) are scheduled for the following Saturday, Sunday, and Monday at St. Louis' Busch Stadium.