The St Mary's Stadium outfit have impressed this season with a series of fine performances to secure a top-10 finish in the Premier League.
However, rumours have consistently suggested the club's top stars including playmaker Adam Lallana and full-back Luke Shaw will depart in big-money moves in the close-season, while manager Mauricio Pochettino has also been linked with jobs elsewhere.
Executive director Les Reed last week moved to quell speculation of a fire sale, and Fonte has called for those claims to be backed up by retaining the club's best players and adding quality to the first team in order to push for European football next term.
He told The Daily Echo: "Yes (it is a crucial close-season), definitely so. We will wait to see what is going to happen.
"Of course (top six) is the aim, but we need to see what happens this summer. If the club decides to go for it or not.
"We want to be successful and to push forward for better things so let's hope that they (the board) can match the ambition of the players.
"Of course to get better we need better players than we have. There is no point in bringing in lower quality.
"We need to bring in top quality for us to fight for the top four, otherwise it is very difficult."
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