The technical committee of the league Friday approved the change to the squad.
Pace bowler Pattinson is currently receiving treatment for a side strain that will rule him out of the tournament.
Worrall, 22, made his Bupa Sheffield Shield and RYOBI One-Day Cup debuts for South Australia in October and took three second innings wickets in the Redbacks' drawn Shield match against Queensland.
He also had a cameo in Nine Network's Howzat mini-series, playing the on-air role of Aussie paceman Mick Malone.
The first round of the Big Bash League starts Saturday night with the Melbourne derby between the Renegades and Stars at the Etihad Stadium here.
