The pair infamously fell out during their time together at Real Madrid and the Portuguese is astounded that the goalkeeper will earn a reported €2.4m net.
Chelsea boss Jose Mourinho has blasted Porto's decision to sign Iker Casillas on a lucrative contract.
Casillas announced earlier this month that he was leaving Real Madrid to move to the Dragao on a two-year deal, with the option of an additional 12 months.
The Spain international is set to earn a net salary of €2.5 million, much to the disbelief of Mourinho, who infamously fell out with Casillas during their time together at the Santiago Bernabeu.
The Chelsea boss was also left aghast at the size of the fee Porto agreed with Marseille for midfielder Giannelli Imbula.
"I cannot believe that Porto have paid €20m for Imbula and are paying Casillas an incredible salary," Mourinho told The Guardian.
"This kind of spending breaks all rules."
Mourinho dropped Casillas during his three-year spell in charge of Madrid between 2010 and 2013, replacing the club captain in between the sticks with Diego Lopez.
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