Pato turned his ankle on the turf during Sunday's 1-0 victory at Fiorentina, while Kaka's spokesman Diego Kotscho warns a knee problem has been dragging on for months and "he probably will not be fielded against Arsenal."
"Pato is much better today. Up until yesterday he was walking with the aid of crutches, but now he can walk without feeling any pain," he told Milan Channel.
"We are confident of his recovery time. Up until yesterday we thought it would take two or three weeks, but now I think within a fortnight he can be recovered and ready for the match with Arsenal."
There were fears Pato had damaged ligaments or even fractured his ankle when he caught his studs in the turf.
"Pato was certainly very frightened, as it was his first injury and came after scoring a fantastic goal the day before he was set to join the Brazilian national team. It was a physical blow and a psychological one."
The race to play at the Emirates on February 20 is also on for Kaka, who has been struggling with a knee problem.
"Kaka will certainly be available against Arsenal, but he won't be there with Siena," confirmed Meersseman.
"This knee injury has been going on for almost two years and he always feels a little pain the day after a match. This is why we decided to take action so he can recover quicker in future."
