The 21-year-old Australian, who missed two months earlier in the campaign with the pelvic problem, has been receiving treatment this week after the injury inflamed again.

The news is hardly what Socceroos boss Pim Verbeek would want to hear two months out from the World Cup.

But Middlesbrough, who are making a late push for promotion via the playoffs, are desperate to keep their stars on the pitch.

"Rhys hasn't trained this week," Strachan told the Middlesbrough Evening Gazette. "He has been carrying an injury.

"I know what it's like. I had to keep playing with a hernia operation once when I was a player.

"It's not easy, so it's brilliant that Rhys is ready to go again on Saturday. He has done fantastically well to keep playing.

"If we had more midfield players, then we could make changes and give players a rest when they need one.

"But, at the moment, I really can't do it."

And Williams' Australian teammate at Boro, Scott McDonald, has urged the side to continue their push for promotion which has seen them go eight games unbeaten and within four points of stuttering Swansea in sixth spot.

"The gap is four points now; that's do-able," said McDonald, who has scored two goals in Boro's last three matches.

"There's two teams above us who are under a lot pressure to right now and if we can win at West Brom, they will really start to feel the heat.

"Swansea looked really comfortable a few weeks ago and we never looked like catching them but now they have gone off the boil a bit and they are looking a bit vulnerable.

"And Leicester aren't out of reach yet. They won last weekend so they are a bit further away now. It is six points now and you think that they should be clear but you never know.

"If they lose one of their next two and we keep winning ours, the gap closes - and we've still got them to play.

"Plus our goal difference is still good enough to catch both of them if they slip up. There's a lot of ifs and buts in there but you never know.

"All we can do is keep winning and see where it takes us."

Middlesbrough travel to promoted West Bromwich in Saturday's late kick-off in the Championship.