The Newcastle Jets will seek immediate defensive reinforcements if Lachlan Jackson's ankle syndesmosis injury is as bad as feared.
Centre-back Jackson has already been ruled out for the next four weeks but could miss up to three months, with "inconclusive" scan results leaving the 21-year-old in limbo.
Coach Mark Jones expects to know more next week but says he will look for a second injury replacement player if Jackson, who suffered the injury in the first half of Newcastle's draw with the Western Sydney Wanderers last weekend, is out for the longer term.
"It's a difficult injury to diagnose early," Jones told reporters on Thursday.
"Hopefully Lachie's only four or five weeks away but if it doesn't heal the way we think it's going to heal, it could be 10 to 12.
"We've just got to wait and see."
A possible candidate to replace Jackson would be former Socceroo Jon McKain, who is set for an imminent return home after two years with Malaysian club Kelantan.
The Jets have already signed one injury replacement player this season in versatile 18-year-old Johnny Koutroumbis, who came in last week as cover for Daniel Alessi (knee).
Jones knows Koutroumbis from his time as Adelaide United's youth coach and said he wouldn't be afraid to hand him an A-League debut off the bench against Sydney FC on Saturday.
"He was one of our best players in Adelaide and hence why he's here - he's a good athlete, he's calm on the ball, he's good in the air and I think he's got a lot of talent," Jones said.
"It's a big ask for him to come in and play Sydney FC in his first game in the A-League. But he's looking tidy and I'd be comfortable to play him."
Newcastle are also without goalkeeper Ben Kennedy (Achilles) for the season and winger Andrew Nabbout (groin) for the next three to four weeks.
However, Finnish striker Aleksandr Kokko is fit, although Jones has made it clear he won't just waltz back into the team.
"It's just a matter of him forcing himself into the side," he said.
"We've obviously got a decent bench at the moment so it's not a case of if he's ready he comes straight back in -- he has to earn his way in the squad."