Leinart got upset at the former Superman actor when Cain went on camera and warned Johnny Manziel to tone down the Hollywood partying or would end up like Leinart.
Dean Cain says he feels bad Matt Leinart got so upset with him last week -- saying the only reason he was critical of the former NFL star is because he expected him to have a better career.
The former USC QB fired back on Twitter -- calling Cain a D-lister who couldn't hack it in the NFL.
Now, Cain is apologizing ... sorta ... saying he's "Sorry Matt got offended."
Then came the backhanded compliment -- "As a fan of his, I was hoping for a more storied career."
The shots continue -- Cain says he's not mad at Leinart's insult because he's got thick skin and can take criticism ... unlike some other people.
Bottom line -- don't expect to see these guys having dinner together anytime soon.