Franjic hurt a hip late in Australia's 2-0 semi-final triumph against United Arab Emirates on Tuesday night.
"It's a final of a major tournament. I reckon unless they chopped his leg off, he would put his hand up to play," Postecoglou said.
"So we'll see how he settles down. I'm sure a few of the boys are sore, it was a tough game."
Franjic has played every game of Australia's campaign, which culminates with the final against Korea Republic in Sydney on Saturday night.
Postecoglou said making the decider wasn't cause for celebration among the Socceroos, who were beaten cup finalists four years ago.
"There's no champagne corks being popped, they're already in recovery mode," he said of his players.
Postecoglou praised the Socceroos' complete performance in the triumph against the Emirates which featured two early goals, slick teamwork and sturdy defence.
"Everything is on the line when you get to this point, and you know that one moment could change everything and deny you an opportunity to play for the title," he said.
"We got a great start. I thought we looked dangerous from set pieces the whole night ... but we defended really, really well - our defending was really brave, we kept a strong line."
Meanwhile, midfielder Massimo Luongo's stunning ascension from fringe to frontline continued with another commanding performance.
Luongo was awarded the man-of-the-match gong, his second of the cup after his acclaimed display in the tournament opener.
Asked if he was surprised by his achievements, the 22-year-old who plays with Swindon Town in England's third tier replied: "A little bit, a little bit. I know within myself what I'm capable of.
"To be fair, it has only been tested at (English) League One level, so to bring it out on the big stage like this is a little bit surprising.
"But I feel like that I'm getting away with a lot. Maybe I should be believing in myself a little bit more.
"And maybe I can do a little bit more in the next game."
