AC Milan CEO Adriano Galliani says that Real Madrid misfit Kaka needs to agree a switch to San Siro on Sunday for the transfer to come through.
The Brazilian moved to the Bernabeu from the Rossoneri in 2009 but struggled to make an impression during his four years in Spain.
He confirmed that he wants to leave the club earlier this week, with Galliani now in Madrid to thrash out a deal with the player.
"The arrival is difficult," he told reporters.
"I'm here. It's tough, we'll see. He has to say yes tonight because he'd need to be back in Milan tomorrow for a medical."
Kaka represented Milan for six years, winning the 2007 Champions League with the club and claiming the Ballon d'Or that year.