The Rossoneri sold the Swede to Paris Saint-Germain this summer for around 20m, but Barcelona's financial report presented on Friday suggests his original 2010 move to San Siro has not been paid for yet.
"The club need to be cautious if they are to be able to take on ambitious future projects," said Vice-President Faus said.
"We have to look to the medium- and long-term stability of the club. Rational and austere measures need to be applied in order to secure a positive balance sheet.
"The club must reduce the debt to sustainable levels and, above all, not take on more debt. We have to prepare for what could happen in the near future and have stronger assets. For ambitious real-estate projects, we need a healthy balance sheet."