"I fully recognize the seriousness of the situation involving my former teammate, and I regret that my actions appear to make light of that serious situation. I apologize to anyone who was offended by my actions," he wrote in a link that was tweeted to his Twitter followers.
A source told ESPN.com's John Clayton on Sunday that the Steelers had planned to talk to Pouncey about the photos. It is unknown whether that discussion had taken place before Pouncey posted his apology.
Mike Pouncey hasn't yet posted a similar apology. A source close to the center told ESPN.com on Sunday that the Dolphins were expected to discuss the photos with him, however.
The Pouncey brothers, who are twins, reportedly wore the hats on Saturday at a Miami nightclub, where they were celebrating their upcoming birthdays. They both turn 24 on July 24. The photos, which began circulating on the Internet on Sunday, do not appear to be digitally altered.
A Dolphins spokesman told the Miami Herald on Monday that the team had "only recently heard about it" and would not have any further comment on the matter.
The brothers played with former New England Patriots tight end Aaron Hernandez at the University of Florida. They were with Hernandez at the Venue nightclub in 2007 on the night of a shooting that left two men wounded. Hernandez was briefly questioned by police after the shooting, but at the time they did not see him as a suspect.
Hernandez is charged with the execution-style murder of 27-year-old semipro football player Odin Lloyd and is being held without bail. He has pleaded not guilty. The Patriots released the tight end last month after he was arrested.
Information from ESPN.com's John Clayton was used in this report.