McDonald, who underwent hernia surgery whilst with Celtic in early January, had started the last four games for new club Middlesbrough but is still feeling discomfort and struggling for fitness.

The 26-year-old Australian was sent to see a specialist and the results of the visit will decide if McDonald needs a period of rest.

Boro boss Gordon Strachan believes the Socceroo may have rushed his comeback from injury, in eagerness to impress his new club who he's yet to score for.

Strachan said: "We're having to look at his stomach. He's had his op and it's never cleared up and he's in discomfort.

"He's away today (Friday) and we'll decide whether he needs to get some rest or he can play on.

"He's definitely nowhere near fit. I think he pushed himself too early, to be honest with you.

"He played with an injury and we won two games and lost two.

"Sometimes you take a risk. You never know. But his enthusiasm is overwhelming, that's for sure."