The former AC Milan defender has been on trial at Finch Farm in recent weeks, featuring for the U21 side against Norwich in September, in an attempt to earn a permanent deal.
The 27-year-old has signed a contract until the end of the season but will prove his fitness at Doncaster first before getting the chance to wear a blue shirt.
Mattioni, who began his career with Gremio, is a free agent after being released by Espanyol over the summer. Mattioni made just 16 appearances for the club in five years due to injury.
He suffered an anterior cruciate ligament injury in his left knee in 2010 just months after signing for the club, missing the rest of the season. Then on his return he suffered the same injury in his right knee, ruling him out for nearly two years.
Mattioni could make his Doncaster debut against Colchester on Saturday and Evertonians will be watching with interest to see whether the Italian can prove his fitness and maybe even return to challenge for a first-team spot at Goodison.