Chicago Cubs pitcher Matt Garza experienced some tightness in his side while rehabbing and likely will miss the first month of the regular season.

Garza, sidelined since Feb. 17 with a strained left lat, will be shut down for one week, according to manager Dale Sveum.

Sveum also announced that Jeff Samardzija will be the team's Opening Day starter.

Garza missed the last 2 1/2 months of 2012 because of elbow problems. He went 5-7 with a 3.91 ERA in 18 starts last season.