Robson picked up the injury in Saturday’s match with Sydney FC, just seconds before the home side opened the scoring, and limped off in obvious distress.

The United coach had earmarked the  24-year-old to fill the void left by Jason Culina during his skipper’s spell with the Socceroos at the Asian Cup.

But he will now seek a replacement as he looks to bolster his squad for the push towards the Finals Series.

“It’s not a lucky period for us," said Bleiberg. "Robson has had his injury problems in the past but we nursed him through and used him sparingly knowing we would need him while Jason was away.

“He injured his hamstring against Sydney and the likelihood is that it will sideline him for the majority of the season.

"We are hopeful of signing (Nuremberg midfielder) Peter Perchtold but Peter is more a central midfielder than a playmaker.

“Time is against us a little at the moment but we will certainly be looking at some options. If we can find a replacement for Robson, someone who can perform in that playmaker role, then that’s the course of action we will take.

“If the right player comes along then the door is open, not just for the rest of this season, but possibly next season as well.”