The joint Eastern Conference leaders host the region's second-bottom side on Saturday but Australian star Cahill is still in doubt as he nurses ankle ligament damage sustained in the September 1 win over DC United.
"I'm not planning on Tim starting, I'm not planning on it," said Petke.
"It's not unlikely, but I'm not planning on that. But perhaps he could be coming off the bench or perhaps we're going to rest him one more week.
"It's one of these things we don't need to make a decision right now. We have all the way up to Saturday at 7 o'clock."
Cahill has been in solid form in recent times, scoring four goals in his past six outings, despite carrying knee and ankle injuries.