After Tuesday's 5-2 victory over the Padres, Mattingly said Dietrich was expected to be fine. He noted that the infielder is available to pinch-hit, and could be ready to start in a few days.
Miguel Rojas started at second base on Tuesday.
Dietrich has taken his share of punishment. He's already been hit by pitches 10 times this year. No other Miami player has been plunked more than twice.
Dietrich was clipped on his back foot by Padres reliever Brandon Maurer in the sixth inning.
The team record for most hit by pitches in a season is 17, held by Carlos Delgado in 2005.
Alex Gonzalez holds the franchise career mark for hit by pitches with 51 from 1998-2005.
Dietrich already has been struck 40 times, which is tied for fourth most.
Along with being hit by pitches, Dietrich also was clipped by a foul ball in the back of his head while sitting in the dugout, waiting to bat, at Atlanta on May 29.
Mattingly seemed optimistic Dietrich might not only miss a couple of days, even if the X-ray reveals a fracture.
"Even if it is something, you can't do a whole lot for it," Mattingly said. "It's just a couple of days and be ready to go."
Joe Frisaro has covered the Marlins for MLB.com since 2002. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro. This story was not subject to the approval of Major League Baseball or its clubs.