Del Piero didn't train with the bottom-placed Sky Blues on Thursday as he continues to recover from a hamstring injury that kept him out of last week's 2-1 win away to Wellington Phoenix.
Farina said he would give Del Piero until just before the match at Allianz Stadium to prove his fitness.
"You'd like to be in a situation where there was no question about him playing, but there is still that little bit of doubt there," Farina said. "But we've still got 48 hours."
After ending their five-game winless streak last week, the Sky Blues will be boosted by the return of Terry Antonis and Brett Emerton, who missed the past two matches while on national team duty in Hong Kong where the Socceroos qualified for the East Asian Cup.
Farina indicated it would be tough to drop anyone involved in the win last weekend.
However, he will be without defensive midfielder Terry McFlynn as he serves a one-match ban for being sent off last week, with Emerton, Antonis or Hagi Gligor the likely contenders to replace him.
"No one really deserves to miss out from last weekend, but that decision will be made tomorrow after the final session," Farina said.