The Argentine midfielder lost his cool after referee Steve Bennett dismissed him in the 3-0 defeat.
But Defoe escaped with just a booking - and Bennett took charge of that game too.
Mascherano told The Sun: "I was bitten! That's the worst thing I've been involved in since I've been here.
"What is strange is that the ref didn't send off Defoe that time. He was next to me and saw everything and even so he didn't get out the red card.
"I'm not a violent player. I've only been sent off three times in my career."
Mascherano, banned for Sunday's derby with Everton at least, said: "I insist I still don't know why the ref sent me off. I never hurt him. But I'm sad about it as I left my team a man down."