The 38-year-old World Cup winner will miss the New Year's Eve clash with Adelaide United on Monday after being targeted by defenders during Sydney's shock 1-0 win over the league-leading Central Coast Mariners on Thursday.
"He got fouled eight or 10 times during the match and with the short turnaround he hasn't been able to train and he's not fit to play," Farina told reporters on Sunday.
"It's a blow for us and a shame for the people of Adelaide but I think there needs to be better protection for him on the field.
"We play a physical game and Alessandro is a big boy who can handle himself but he is getting kicked repeatedly and if that continues he will miss games through injury."
Although signed in the off-season to much fanfare Down Under, Del Piero has endured a dismal season at struggling Sydney despite his best efforts, and has missed matches due to a hamstring strain.
Del Piero has already complained about the treatment from defenders he has received while playing in a losing side, fuelling speculation the club's marquee recruit may elect to forgo the second-year option on his contract.
Sydney lie second-bottom of the 10-team league at the halfway mark of the 2012/13 season, and face a Herculean task to qualify for the playoffs in April.
(Reporting by Ian Ransom; Editing by Greg Stutchbury)