The Millwall goalkeeper was shown a straight red card eight minutes into Saturday's FA Cup fifth round clash with Crystal Palace.
Roberts raced out of his box before colliding with Mateta as he cleared the ball away.
His boot connected with the Palace striker's head, causing him to be stretchered off and taken to hospital.
Mateta has since been discharged after requiring 25 stitches to his ear.
Simon Jordan has now slammed Roberts for his challenge as he faces the possibility of an extended ban.
READ MORE IN FOOTBALL
Wayne Rooney wants veteran former striker at Man United as Zirkzee and Hojlund struggle
Frank Lampard reveals unseen role Pep Guardiola has played in Coventry success
The former Palace chairman reflected on the incident on White & Jordan, explaining: "Do fellow professionals have a duty of care to one another? Possibly. Do I think it was a pretty diabolical challenge? Yeah, it was.
"Did it ruin the game potentially for Millwall? Possibly. Because ultimately it takes their goalkeeper, they go down to 10, it makes it less of a competition.
"It was a rash, it was a rash challenge. I don't know the malice, only the man himself can know the intent side of things.
"There's a part of me that thinks there's a cowardly way to go as a goalkeeper, but I suppose if you're 10 yards out of your box, you can't go with your hands.
Most read in Football
Truth behind claims Ronaldo is facing 99 lashes and can't travel for Al Nassr's next match
Shock club plot Cristiano Ronaldo transfer talks as Al Nassr contract set to expire
Newcastle star sent off and will miss Carabao Cup final after complete headloss
Wayne Rooney wants veteran former striker at Man United as Zirkzee and Hojlund struggle
"But the fact of the matter, you're going with your feet that high, there's only really one likely outcome, or two, you're going to get the ball and be lucky to get it, or you're going to get a player. And he got a player. And it was a poor challenge."
Millwall boss Alex Neil denied that his goalkeeper had intentionally injured Mateta.
Following the match, he said: "He's tried to get the ball, he's mistimed it and caught the lad. It's no more than that from my perspective.
"He has certainly not intended to hurt the player or anything like it. We wish Mateta the best and hope he gets back on the pitch."
Roberts was sent off by referee Michael Oliver after a VAR review of the challenge.
Palace went on to secure a 3-1 victory, with an own goal from Japhet Tanganga followed by Daniel Munoz and Eddie Nketiah strikes.
Oliver Glasner's side will now face Fulham at Craven Cottage in the quarter-finals on the weekend of March 29.
Roberts currently faces a three-match ban, missing the Lions' Championship clashes with Bristol City, Watford and Leeds.
That's really dangerous' - Jean-Philippe Mateta rushed to hospital after horrible Millwall challenge
However, he could see his suspension extended with the FA considering a longer ban based on the grounds of 'clearly insufficient' punishment.
The 30-year-old has made six appearances for Millwall since signing from Middlesbrough in the summer.
He has largely served as deputy to Neil's first-choice Lukas Jensen, with Roberts limited to just one league start.