The Slovenia Under-21 international has joined on a free transfer after leaving Italian side Ascoli.
The 20-year-old came through Milan's youth academy and spent a month on loan with Leeds in 2014-15, making two appearances as a substitute.
Benedicic has also played for Serie B side Como and featured nine times for Ascoli before leaving.
Leyton Orient have signed former Leeds and AC Milan midfielder Zan Benedicic on a deal until January.