Swiss athlete Jason Joseph has apologised for celebrating victory while a rival hurdler was knocked unconscious with suspected head injuries at the European Indoor Championships.

Spaniard Enrique Llopis took a severe fall on the last hurdle, slamming his head into the track in a sickening impact that left him in need of medical attention, including a neck brace.

While he lay prone on the ground, Joseph - who won the race - collected a Swiss flag and celebrated without checking on his stricken competitor.

Joseph consequently copped a barrage of criticism for failing to make sure Llopis was all right, with the Spanish media branding his behaviour 'the most unsportsmanlike action in history'. 

'Was it appropriate to express joy and happiness while another sportsman was laying on the ground unconscious?' an athletics fan posted on his Instagram.

'Seriously, you expressed everything but your egoizm. Zero empathy. You don't deserve this victory. Victory is earned by attitude and you showed absolutely zero attitude,' 

Another claimed that Joseph knew his rival was hurt, but celebrated anyway.

'He did look over but ignored what was going on went and got Swiss flag and posed and smiled etc for the cameras,' the posted.

'Didn't give 2 s***s about the poor fella that was unconscious after falling behind him, he was all about the glory. Really made me sick seeing him celebrating he could have went and checked if he was ok,' another fan posted.

Joseph has since apologised on Instagram and said he was locked into competitive mode at the time of the incident. 

'First things first. I'm sorry I didn't check that you were okay,' he said.

'I was lost at the time. Totally blocked from what was around me.

'I hope you're okay, I see you in outdoor competitions.'

While Joseph received plenty of backlash, there were also others who defended him. 

'Would love to see all the critics in that situation! Always easy to talk, spread hate and assume the worst in people... Congratulations,' one posted.

'You all must be able to have some understanding here. It's not okay to give him so much hate now. You must be able to understand that he just won a title he wished for all his life which is an overwhelming moment for him. You can't just call him a bad person now,' added another.

'Sorry for Llopis. It was very unfortunate that he had this crash and hope he's well, but you folks have so much hate for a kid who won, although he have sad how sorry he was and still is, that you almost blame him for causing the crash of your athlete,' posted another fan.

'I wish Llopis well, but you folks should stay in your negativity. Some of you have done worse, but you come here talking hate.'

Llopis' condition appeared to have improved as he later appeared in a video posted on the official Twitter account of the Royal Spanish Athletics Federation. 

In the video, he expressed his gratitude towards the Federation and medical staff for their assistance, and shared that all the tests came back fine. He also shared his optimism towards his recovery, stating: 'Now it's time to recover.'