Sydney FC have been dealt a major blow for Friday night's season-opening clash against Newcastle at Allianz Stadium with marquee star Brett Emerton almost certainly out with a back injury.

The 34-year-old pulled up in the final minutes of Wednesday's training session at Macquarie University after feeling his back seize up. Emerton now appears highly unlikely to be risked against the Jets, adding to an already-large list of unavailable players.

Sydney FC's Brett Emerton is in doubt for Friday's clash with Newcastle. Credit:Getty Images

“It's an ongoing problem with Emo and we thought his back had settled down pretty quickly but we'll see tomorrow [Thursday] how he wakes up,” Farina said. “He was just running along and I saw him seize up, so I stopped the session. An hour later he was better but we probably won't know until tomorrow.”

Asked if he was prepared to roll the dice with the former Blackburn defender, Farina admitted it was unlikely. “I'd rather not play any player who isn't 100 per cent fit,” he said. “We've got the cover available and I wouldn't want to go into the first game of the season with even one or two players in doubt. I wouldn't risk that.”