The combative midfielder admitted that the Rossoneri are going through a difficult financial situation and stated that coach Massimiliano Allegri is in for a rough ride
The 34-year-old, currently on the books of Swiss side Sion, did not have his contract renewed at the end of 2011-12 as the Rossoneri look to revamp their squad in the summer.
With Milan's financial problems well documented, the Italian giants have been forced to sell Thiago Silva to Paris Saint-Germain, with Zlatan Ibrahimovic expected to follow the Brazilian defender shortly.
"Without Thiago Silva and Alessandro Nesta, Milan's defence no longer has any reference points," Gattuso told La Gazzetta dello Sport.
"Ibrahimovic alone wins you at least 10 matches per season. If I were Massimiliano Allegri, I would have trouble sleeping.
"Milan cannot play in the Champions League just to participate and to watch such a revolution in the squad after so many years is a true shock."
Gattuso then urged president Silvio Berlusconi to explain in detail the club's strategy to the fans.
"You cannot criticise Berlusconi after what he has done in the last 26 years, but he has to be clear and tell fans how things are," he added.
"He must say if sacrifices will be made for two or three years and then there will be a return to spending.
"If people are losing their jobs, then there is no need to spend money on a football club.
"Even Inter are tightening their belt. Juventus are the only club who are spending and they recently built a new stadium."
The former Italy international then called on Milan to emulate the Serie A champions and heaped praise on Bianconeri coach Antonio Conte.
"The slogan for this season must be to fight and to imitate last season's Juve, which was built on two champions: Andrea Pirlo and Gianluigi Buffon," Gattuso noted.
"All the others threw up from working hard. We see that Conte has a sickness for football.
"When we played against Juve, everyone spoke of Edgar Davids, but Conte would grind out the kilometres and would never give up.
"He was like a cat attacking your chestnuts, as they say where I come from."