The Pirates would likely recall Diaz if Francisco Cervelli (foot) is forced to miss time.
Diaz made his first start in the majors Sunday before Pittsburgh returned him to Triple-A Indianapolis. The catcher recently returned from elbow surgery and has played in only 15 games in 2016. He has offensive potential -- he batted .328 in 326 Double-A at-bats in 2014 -- but it remains to be seen how much he would play.