The France international freely admits that the Rossoneri have lost "two great players", and has called for Massimiliano Allegri's men to stand up and be counted
The Rossoneri's Serie A title hopes are already being written off by many pundits after being forced to cash in on their most prized assets because of the well-documented financial problems at the club.
And Mexes believes that the players must ignore all of the pessimism currently swirling around San Siro and just look forward to the new season.
"We have lost two great players, but the important thing now is to think of all the games awaiting us," the defender told Milan Channel. "We must again prove that we are Milan, a competitive Milan."
On a personal level, the Frenchman is focusing all of his energy on getting himself back in peak physical condition after his summer holidays.
"In pre-season, you need to work so much; we must put ourselves in a position to be ready for the new season," the former Roma man reasoned.
"I had a month off after the Euros and I have to be at my best before the start of the championship. I have to give my all, like all my team-mates."
The 30-year-old, who played three games in Poland and Ukraine, joined Milan from the Giallorossi last summer.