Martin Keown was left fuming with the handball rule after Arsenal conceded a controversial penalty which cost them.
Inter Milan were able to take advantage in their Champions League clash after Mikel Merino was punished for handling the ball in the area. Hakan Çalhanoğlu opened the scoring for the Italian side shortly before half-time came around with several questioning the referee's decision.
Inter put a free-kick into the box and the ball was flicked on with Merino, who was going to block the ball, seeing it hit his arm. The Spaniard was only yards from Mehdi Taremi, who had knocked the ball forward, and many felt the proximity may save him.
Keown bemoaned the different interpretations across Europe with the Premier League applying slightly different rules to the Champions League. The English top flight has a higher bar for giving penalties and the ex-Arsenal man was unhappy with the decision - which ultimately decided the game.
He said on TNT Sports : "Is the arm in an unnatural position? and it isn't. I mean I don't know who determines that, VAR is never going to intervene, and then we have this debate again. I think it is ruining our game - it certainly ruined Arsenal's half-time team talk. I think they're hard done by there."
Rio Ferdinand added: "It is unfortunate that the rules are different in different competitions. I think that is the confusing thing, not only for players but for fans and pundits."
Bukayo Saka, the Arsenal skipper, was quick to question the decision but the referee stuck by his original call and allowed the Italian side, who are yet to lose in the competition this term, to take the lead.
Heading into the contest both Arsenal and Inter had claimed seven points from their opening three Champions League games. The Gunners are currently trying to rid of some poor form that had seen them win just two of their five games before heading to Milan.
In the Premier League they've picked up just one point from the last nine available with a loss at Newcastle their most recent reverse.