Walter Smith has admitted his frustration with the failure of Kris Boyd to stamp down a regular place in his Rangers team. In spite of the outstanding record of 74 goals in 83 starts for Rangers, Boyd is regularly consigned to the bench for Old Firm and European ties.

"There is no doubt he is the biggest enigma I have encountered," Smith told The Herald. "There have not been many, if any, who have that specific ability of goalscoring, which is so high, but is linked to a level of play that does not come anywhere near that.

"He has played long enough for everybody to form their opinion: everybody knows exactly what he can and cannot do.

"I have said to him he has reached the stage where he has to make an assessment of his assets and understand the managerial aspects as well."

Smith is reluctant to get drawn into the debate opened up by Boyd's refusal to play under Scotland boss George Burley.

"I hope this will be the end of it because it becomes tiresome," he said. "I think it will be an issue for any manager because of the frustration he brings.

"A number of managers who have had him in their team have thought along the same lines. At Rangers, he has worked harder this season than any other since I have been here. He realises he has to do more."