First it was Travis Dodd and Mathew Leckie battling to be fit for the crucial Melbourne Victory clash on Friday, and now Mullen has been struck down ahead of  the club’s biggest test of the season so far.

The defender, who turns 21 today, went straight off the track to ice his ankle after rolling his ankle.

United Head Coach Rini Coolen is not holding his breath on Mullen’s availability, almost conceding he will be without the right back.

“It’s not positive I think,” Coolen said. “From what I saw he rolled his ankle and we have to wait to find out exactly what is going on, but I think he will be out for the upcoming game.

“It’s not good because it’s also his birthday today, so that’s not a good moment.

“Definitely we can’t play with him in our next game, when something like that happens in training, you’re not happy with that of course, but we have to handle these things and that’s what can happen sometimes in football, so things aren’t positive for him. 

“Let’s hope it is maybe just one game, but you never know and that’s what we’ve got to find out in a couple of days.”

Mullen’s likely absence leaves Coolen with an unwanted headache as he tries to plot the downfall of the Reds’ bogey team.

Earlier this season Coolen had the luxury of calling on Cameron Watson to come in at right back and impressed in his ten game stint with the club.

But with Watson’s temporary contract having ended after the Week 10 draw with Gold Coast United, Coolen must shuffle the deck that he has at his disposal and find a suitable replacement.

“Normally when Daniel wasn’t there that was a position for Watson…but he’s not here, so we’ll find out how it is with Daniel and see what we can do,” Coolen said.

“You have problems when you lose players like (Joe) Keenan and Watson. I wasn’t happy with it, normally there is always a problem when you lose a player like Daniel Mullen, but if you have players in your squad that can play in that position, like Watson, then it is not a big problem.

“We can’t but maybe we can do something in a couple of days, but let’s just hope the problem for Daniel is not so big.”

Meanwhile, Dodd (Achilles) and Leckie (knee) were on modified programmes at training this morning.

Coolen said  the they are both making steady progress, but it will all depend on whether they come up for training with the main group in the Reds’ final session on Thursday.

He added: “They’re on the schedule that we told them to do…so they’re progressing much better every day so it’s positive.

“Normally if they are fit Wednesday, then they have to train with us Thursday, and if they are fit Thursday, then maybe they can be involved in the game on Friday.”

The club expects to find out Mullen’s prognosis later today.