The Argentina midfielder scored for the Reds in Sunday's 3-1 loss at Craven Cottage.
Mac Allister said afterwards: "I think in the first half we had 25 or 30 minutes where we couldn't find ourselves. We made a lot of mistakes that we normally don't do. That's why we lost this game. They scored three goals, we got punished and after it was really hard to come back.
"When you get to this stage of the tournament every mistake you do is hard and you get punished. I'm pretty sure that we have a team where we have a lot of players with experience. Today wasn't a good experience. But I'm pretty sure we will come back stronger and in the next game we will show what we can do."
He added, "I think there is going to be a lot of people saying that this Premier League is done, but in the dressing room we know that it's not. We still have a lot of games coming up and all of them are really difficult in a league like this.
"Everyone is fighting for something. We have to make sure that we play the way we know and play the way we want and not make the mistakes we've done today."