After falling further behind on aggregate through Neymar's cool finish for the Catalan giants, Alex Iwobi attempted to work his way into the penalty area for the Gunners only to fall to the ground after a coming together with Javier Mascherano.
Replays showed that the youngster clipped the back of his own heel as he went down, but the footage was inconclusive regarding any contact from the Argentine defender.
Despite any infringement from Mascherano being minimal, Webb feels that the North London outfit had grounds for a spot kick, which could have resulted in the first of the four goals that they required to remain in the tie.
Webb said: "I think that Iwobi is very unfortunate. It doesn't have to be intentional. Mascherano got too close to Iwobi and it was careless."
However, speaking on the same channel, Arsenal legend Ian Wright insists that it would have been harsh on Mascherano if a penalty had been awarded.
Wright said: "I don't think it was. Iwobi is having a fantastic game and I am really pleased for him but Mascherano hasn't made any motion to try to challenge him.
"If anything, Iwobi has maybe clipped his shin and his leg has caught himself. I don't think it was on purpose."
Manager Arsene Wenger had handed Iwobi a surprise start in the Arsenal attack, with his only previous experience in the Champions League coming in a five-minute cameo against Bayern Munich earlier in the season.