US Open 2015: Jason Day collapses on final hole of second round before being taken to hospital for further tests on vertigo symptoms

Day collapsed as he followed his tee shot on the ninth but managed to regain his feet to finish the hole after treatment

Jason Day receives treatment after collapsing during the second round (Getty Images)

Jason Day collapsed in a dramatic episode while completing the final hole of his second round at the US Open.

The Australian was walking after his tee shot at the ninth when his legs suddenly went from under him as if struck by a blow.

It was initially thought he had turned his ankle on the banking but when his caddie rushed to his aid it became clear there was nothing wrong with his limbs.

Day had been suffering from vertigo symptoms for weeks but exhaustive tests including MRI scans revealed nothing.

“I had three sleep studies done,” said Day on the eve of the tournament. “I had a lot of blood tests done. I had an MRI on my head and my back and my neck. And everything came back negative. So I have no idea what that was, other than I just may have been exhausted.

“I was training so hard coming into tournaments and then on top of it I was doing practice, playing competitive golf and then trying to balance that with family as well. It's just a full-time kind of gig there.

“I think I just ran out of gas. I wasn't feeling good, so I had the shakes and the tingling up my arms. And the loss of energy and strength was probably caused by that.”

Day was struck down similarly at the WGC-Bridgestone Invitational at Firestone last August and was forced to withdraw from the tournament. Here he was able to resume his feet after treatment from medics and complete the hole, albeit shakily.

He was then taken to the medical centre on a buggy before heading to hospital for tests.

Jordan Spieth, who was playing in the same group, said: “I turned around and he was lying there. All I heard was that it was dizziness. He could barely walk when he got up so for him to finish the round was pretty strong.”