Strasburg is likely to start for the Nationals, a source told MLB.com. A pitching change from earlier announced starter Tanner Roark has not been confirmed by the team.
Game 4 at Wrigley Field was postponed by rain Tuesday night, giving the Nationals a chance to start Strasburg on regular rest being down 2-1 in the best-of-five series.
However, manager Dusty Baker made a surprise announcement when he said Roark would still start because Strasburg was "under the weather."
The Cubs will turn to their scheduled Game 4 starter, Jake Arrieta, on Wednesday looking to finish off the series.
Strasburg held the Cubs without a hit for 5 2/3 innings in Game 1 before Chicago pulled out a 3-0 victory.
Baker told reporters Tuesday night that Strasburg would start Game 5 if the series went that far.
"It's fine," Baker said. "We have full confidence in Tanner."