The Australian striker, who joined Middlesbrough from Celtic for £3.5m in late January, has been suffering nagging pain after undergoing a hernia operation in early January.

Middlesbrough were concerned the injury may have been seriously aggravated by a rush to get the Aussie in the team.

But a specialist confirmed an injection would be sufficient for McDonald to recover although he'll likely miss this weekend's Championship game with Cardiff City but could return for the crucial following match against fellow North-East club Newcastle.

McDonald told The Northern Echo: "It's felt okay since I had the injection. Hopefully it stays that way and I keep progressing.

"It's frustrating because when you join a new club, you want to show what you can do."

The Socceroo, who is yet to score at international level, is desperate to open his account for Middlesbrough having made four scoreless appearances including one where he missed a penalty.

He added: "I did push myself at the start and didn't do myself any favours but I just wanted to get out there and play. The manager has shown faith in bringing me and I wanted to repay that.

"But there is no point going out if you are 75 per cent fit and not able to get to the ball that extra second sharper than the guy who's marking you.

"That can be the difference between you getting a goal and not. It's been disappointing. I've not lost confidence about it but it's been getting me down.

"So I said ‘right we need to do something about this.' I'd ignored it for a little while but I went to see the specialist and thankfully I don't need another operation and we've gone down the route of having an injection.

"Hopefully with this week off from the training and doing rehab work, nothing strenuous, there will be no reaction and we can move on.

"Whether or not I am ready for Saturday we'll wait and see. It's just a day by day progression.

"The most important thing is if it's not this week we'll look towards the Newcastle game. But whenever I come back it has to be 100 per cent right this time.

"That is the most important thing for me and for Middlesbrough."