Jon Rahm has been forced out of the Memorial Tournament despite leading at the end of the third round after testing positive for Covid-19.

The Spaniard came off the course in Ohio thinking he had a six-shot final-round lead after shooting a sensational 64 - for a tournament record 18-under - but was then informed he had failed a test taken that morning.

Rahm had been allowed to play subject to daily testing after informing the PGA last week that he was a close contact of a Covid case.

The PGA said he had tested negative every time until today and that the player, who is asymptomatic, would now withdraw from the tournament and isolate.

"I'm very disappointed in having to withdraw from the Memorial Tournament. This is one of those things that happens in life, one of those moments where how we respond to a setback defines us as people," Rahm said in a statement posted to Twitter.

"I'm very thankful that my family and I are all OK. I will take all of the necessary precautions to be safe and healthy, and I look forward to returning to the golf course as soon as possible."

Rahm's withdrawal means Collin Morikawa and Patrick Cantlay are now the joint leaders on 12-under par. Branden Grace and Scottie Scheffler are the nearest chasers on nine-under. The winner's purse is $1.6m.

Shane Lowry dropped two places into a tie for 11th after an up and down level-par round of 72.

Lowry hit five birdies, five bogeys and a double, dropping a final shot on the 18th to remain at four-under.

Rory McIlroy moved up to a share of 23rd after a 71, his best round of the tournament so far. The Down man had four birdies and three bogeys.

FULL LEADERBOARD

PGA Tour statement on Jon Rahm

"On the evening Monday, 31 May, the PGA Tour notified Jon Rahm that he was subject to contact-tracing protocols, as he had come in close contact with a person who was Covid positive.

"Per the Tour's Covid Health & Safety Plan, Rahm was given the option to remain in the competition and enter our tracing protocol, which includes daily testing and restricted access to indoor facilities. Rahm has remained asymptomatic.

"Rahm has tested negative every day, but his most recent test - which was performed after the conclusion of his second round (rain delayed) and before the start of his third round - returned positive at approximately 4.20pm (local time) while Rahm was on the golf course.

"The PGA TOUR's medical adviser requested a confirmatory test on the original sample, which came back at 6.05pm, and was also positive.

"The PGA Tour's medical adviser notified Rahm immediately upon completion of his round, and under Tour protocols, he will be withdrawn from the competition.

"Rahm is now in isolation, and in accordance with CDC guidelines, he will need to remain in isolation through Tuesday, 15 June."