CHICAGO -- Astros third baseman Chris Johnson isn't expected to play in Monday's series opener in Pittsburgh after being scratched from the starting lineup Sunday against the Cubs with a muscle strain on his left side.

Johnson said he injured the muscle swinging the bat during batting practice and was tender. He said he's day to day.

"It was one swing," he said. "It tightened up a little bit, and I have a little knot in my left lat. They couldn't rub on it today because it's so sore, but tomorrow I'm coming in and we'll see how I feel."

Matt Downs, who was originally scheduled to start in right field, started at third base. Brian Bixler was inserted in right field. Johnson snapped an 0-for-12 streak by getting two hits on Saturday, going 2-for-3 with a run scored in a 3-2 loss to the Cubs. He's started 70 of the team's 79 games at third base and is hitting .280 with six homers and 34 RBIs.