Ronaldinho rift means Milan's golden boy is on the market

The €100m (£91m) which Manchester City have offered for Milan's Kaka would be tempting for any club, even one whose owner, the Italian Prime Minister Silvio Berlusconi, has a personal fortune of $9.4bn (£6.4bn). But Milan's change of heart about a player previously described by Berlusconi as "not for sale at any price" is not solely about money.

A number of footballing reasons are being put forward as to why the club would be prepared to sell a 26-year-old player who won the Ballon D'Or and was voted Fifa World Player of the Year just two years ago – and why Kaka would be ready to leave San Siro.

There are four main theories: (1) Kaka and fellow Brazilian Ronaldinho, signed last summer from Barcelona, have not gelled as twin three-quarter players behind the striker in coach Carlo Ancelotti's favoured 4-3-2-1 formation; (2) Milan want to bring back the 22-year-old Joann Gourcuff, who is on loan to Bordeaux, and plan to play him in Kaka's role; (3) Milan intend to extend David Beckham's contract through to 2010 and want to use the Englishman in a more advanced role; (4) Kaka is no longer the golden boy at Milan, the mantle having passed to Brazilian striker Alexandre Pato and the tactical approach will be about getting the ball to him as quickly as possible.

Only the first theory really stands up. The mild-mannered and uncontroversial Kaka has gone public several times this season about his dissatisfaction with his duties since Ronaldinho arrived.

The subtext of Kaka's complaints is that he is expected to do too much donkey work – pressing and tracking back – to cover for the unfit Ronaldinho and consequently rarely finds himself in goal-scoring positions.

Ancelotti will not abandon his system, so one of the players will probably have to be sacrificed and, although Ronaldinho is two years older than Kaka, it is unlikely to be the new signing who makes way.

Gourcuff's form this year for Bordeaux – including a goal of breathtaking skill against Paris Saint-Germain at the weekend – has begun to justify his billing as the new Zinedine Zidane and he could be a fitting heir to Kaka in the Milan side.

However, the player's destiny is no longer in Milan's hands. When the club loaned him to Bordeaux – after he had struggled to hold down a first team place last season – the deal gave the French club the option to buy Gourcuff at the end of the 2008-09 season for €15m (£13.5m). It seems inconceivable that they will not take up the option.

The Beckham and Pato theories are the least convincing. The paltry evidence that Ancelotti wants to play Beckham further forward came from one training session this week at Milanello, the team's training ground, where Beckham played just behind the forwards in a practice match.

Whether or not Beckham stays at Milan beyond March, Ancelotti's view is that he is best suited to a deeper midfield role.

After his two goals at Roma on Sunday, including one deft chip after his speed had ripped the home side's defence apart, the 19-year-old Pato is back in the spotlight but his form over the last two seasons has been fitful. His potential is enormous but it is unlikely Ancelotti would build a team around him just yet.