Barca coach Ernesto Valverde has stated Vidal is not for sale.
But Marotta says: "We'll do something, it's an important moment and we want to keep going.
“Vidal is one of our objectives. As for (Tottenham midfielder Christian) Eriksen, the market closes at the end of January.
“We're working hard, but to improve the quality of our squad, important signings are needed and it's for this obvious that there are difficulties."
He added: “There's a lot of speculation right now, we're all active. Generally speaking, you all know very well that you can do tonight what you don't do today."