Gronk mentioned that he had "liquid" in his head as a result of the punishment he endured:
"No lie, I felt my head, I used to have liquid," Gronkowski said. "It used to be thick, like, my head used to be thicker—a centimeter of liquid in some spots. And you'd be like, what the heck? You could put indents in my head."
Gronkowski also noted that he experienced "mood swings," which he attributed to potential brain injuries.
Following the Patriots' Super Bowl win over the Los Angeles Rams in February, Gronk retired from the NFL just shy of his 30th birthday.
He was a five-time Pro Bowler and four-time first-team All-Pro in nine NFL seasons, but he clearly wasn't the same player in 2018, as back, knee and quad injuries seemed to greatly impact him. His average receiving yards per game fell from 77.4 in 2017 to 52.5, which placed Gronk joint-sixth among tight ends after leading the position in that category the previous season.
On Tuesday, Gronkowski held a press conference to announce his partnership with CBDMedic, which produces CBD products for pain relief. During the press conference, Gronk said he wasn't in a good place physically before retirement but left the door open for a return to football if he can get healthy.
Gronkowski, who suffered two Grade 1 concussions during his career, noted Wednesday that he is doing "brain exercises" in hopes of combating some of the damage potentially done by playing football.
Gronk said that the increased knowledge of how head injuries can impact people down the line played a significant role in his decision to retire: "I was aware of what was going on with my body and my mind, and that's why I had to walk away."
With the Pats struggling to find a replacement for Gronkowski at tight end leading up to the 2019 season, there has been constant speculation about a return.
Gronk suggested during his press conference that he doesn't intend to return to football any time soon, which means New England will have to make do with a tight end corps that includes Ben Watson, Lance Kendricks, Matt LaCosse, Eric Saubert, Stephen Anderson and Ryan Izzo.