United won the first-leg of their Europa League semifinal 6-2, having at one stage been 2-1 behind.
After the game, Fonseca said: “I am always the one responsible, I am here to take on all the responsibilities.
"I don't want an alibi, I'm responsible and I don't want to escape my responsibilities."
Asked if his time with Roma is coming to an end, Fonseca added: "Let's see. Now it is difficult to talk, I think we need to be balanced."