The Australian only recently returned from a hamstring injury that sidelined him for six weeks, but he was forced off on Saturday after complaining of discomfort at half time.
Gers chief Alex McLeish has admitted that the Ibrox medical staff have been unable to pinpoint the problem, prompting the club to seek a second opinion.
"At half time, Craig complained that he had no sprint," McLeish told the club's website. "He was finding it difficult to accelerate when closing down or pushing forward with the ball, so we took him off.
"As far as I am aware, there is no strain or pull in his hamstring, but we will have to get the advice of someone other than our own medical team on this one.
"Craig will see a specialist about this problem and hopefully we can resolve it once and for all."
McLeish also revealed that Steven Thompson's knee operation went according to plan, but believes the forward will be unavailable for the next six months.
"We have spoken to the surgeon and he was very happy with the procedure," said McLeish. "It's now a case of rehab for Steven.
"The prognosis is three to six months, so we will expect him back after six months and, if we get him before, it will be a bonus."
