Singh and Mickelson argue over spike marks

The American left-hander had an official complaint lodged against him by former winner Singh, who complained to tournament officials that Mickelson's golf shoes had caused spike marks on the 12th green.

The two players were later said to have had a heated discussion in the champions' locker room over the incident.

"After sitting in the locker room for a while, I heard Vijay talking to other players about it and I confronted him," world number four Mickelson said in a statement.

"He expressed his concerns and I expressed my disappointment with the way it was handled. I believe everything is fine now."

A tournament official told Reuters: "I understand there was a complaint from Vijay and one of our referees was called in to inspect the spikes (spike marks) and to take off any offending burrs.

"Some of the spikes were quite old ones but I understand Vijay wanted something done about it. It was not a problem after that."

Mickelson said he had been approached by two officials at two different times while he played the 13th hole after 2000 champion Singh, in the group behind, asked for the spike marks to be cleaned up.

"They were sent by Vijay to check my spikes because he felt they were unduly damaging the greens," said the 34-year-old. "If that is the case, I am very apologetic and will make every effort to tap down what spike marks I may make in the future.

"Given the wet and slippery conditions, more than a third of the field is using steel spikes."

Masters rules chairman Will Nicholson later added that no further action was taken.

"No, there wasn't a ruling," he told reporters. "We got a call and how it got labelled on to Phil I have no idea.

"One of our officials talked to Phil to see if there was a burr on the side of one of his spikes. He very generously, as you know he would, said he would change them when he got in if there was any problem.

"There wasn't. If there were those spike marks, they were created by a person or persons unknown."