Pierzynski tried to play Tuesday but was a late scratch and was replaced by Geovany Soto. He hasn't played in the first three games of the road trip.
He started just one game against the Chicago White Sox on the recent homestand and then played in all three games against Boston, but had just one hit. In his last start Sunday he went 0 for 4 with four strikeouts. He's batting .263 with four home runs and 11 RBI on the season.
Pierzynski has been bothered by the oblique for about two weeks. He said he dealt with a similar issue last year with Chicago but was able to avoid the DL.
Chirinos, who was acquired from Tampa Bay earlier this year for cash, is hitting .295 for Round Rock with two home runs and 14 RBIs. He has started at catcher, first base and third base for the Express.
Chirinos' only major-league action came in 2011 when he batted .218 in 20 games for the Rays.
Pierzynski has been remarkably durable throughout his career. He's played in at least 128 games for 11 consecutive seasons. This will be just his second DL stint, with the first coming in 2011.