While the Knights again picked up the wooden spoon this season, Salley could remarkably play a key role in the final series for defending champion Sydney.
The addition of the 24-year-old will give coach Terry Butcher some much needed flexibility against the Jets, and ensures Sydney will have a full bench at Energy Australia Stadium.
Salley plays a similar holding midfield role as McFlynn, which means Butcher may not have to sacrifice one of his more attacking players - such as Ufuk Talay, who is returning from suspension, or Steve Corica - to fill the position.
McFlynn could be out for up to two months after tearing his groin just moments before halftime last Friday.
Salley, who moved to Australia in 2005 after fleeing civil war-torn Ivory Coast, became the first African player to be signed to an A-League club when he joined the Knights from Victorian State League club South Melbourne in May last year.
Former Central Coast skipper Noel Spencer, who was dumped by the Mariners after the club failed to make the top four, was also reportedly a target to replace McFlynn.
There had also been rumours Sydney was chasing former Queensland Roar skipper Chad Gibson, although the club denied it had approached either player.
Meanwhile, Newcastle coach Gary Van Egmond today said all the pressure would be on Sydney on Friday despite the Jets needing to win to stave off elimination.
"The pressure, for me, is really on Sydney," van Egmond told reporters.
"They're the reigning premiers, they're doing all the talking. I think, come Friday, we'll do our talking on the pitch.
"Every time Sydney's been talking about something they've been talking about us. I think it's a feather in our cap that Sydney have been talking so much about our players," van Egmond added after Sydney this week claimed it had the wood over Newcastle.
The Jets have beaten Sydney only once in seven meetings over the two A-League seasons.
Feeds