Seven minutes into the South London derby, Lions goalkeeper Roberts flew out of his penalty area and dislodged Jean-Philippe Mateta with his high boot.
The Frenchman required extensive attention from medical staff and was rushed to the hospital, while the Roberts was sent off following a VAR review.
Mateta has since been released from hospital with 25 stitches to a severe laceration on his left ear.
The FA deemed a three-match ban insufficient for the challenge and instructed an Independent Regulatory Commission to review the ban.
Following a hearing, the Regulatory Commission upheld The FA’s claim, set aside the standard three-match punishment, and instead imposed a six-match ban.
Releasing a statement via Millwall, Roberts accepted his punishment while criticising the backlash he has received.
“As the dust settles, I want to address what has been a really difficult week for all concerned, including my family and I," said Roberts.
“Firstly, to Jean-Philippe, who I continue to send my best wishes to in his recovery. As soon as I could, I reached out to Jean-Philippe personally to apologise, and I was thankful to hear back from him that evening that he was OK and reassured me not to worry.
“I am devastated by what happened. I unequivocally accept the red card as awarded and accept my punishment.
"Furthermore, it has been extremely unpleasant to observe suggestions that I intended to harm a fellow professional. I have categorically never stepped onto a football pitch with the intention of hurting anyone.
“Misleading articles and comments have resulted in an unthinkable amount of abusive messages and threats towards my family and I. To the footballing community who know me and reached out with support through this tough time, thank you, I appreciate every single message.
“Finally, I want to say a huge thank you to everybody connected to Millwall Football Club for their continued support. The togetherness throughout this club is unique, and I can’t wait to be back out on the pitch in front of our fans."
Millwall added that while they were disappointed with the decision to increase the ban, they respect the 'process that has been undertaken'.