Kevin Sinfield has warned against making assumptions regarding any link between concussions suffered playing rugby league and neurodegenerative disease.

A study published last year found footballers were at a four-fold increased risk of dying from motor neurone disease than age-matched members of the population.

Sinfield, the Leeds director of rugby has seen his friend and former team-mate Rob Burrow's battle with the disease at close quarters, with his diagnosis being confirmed a year ago.

Since then Burrow has been confined to a wheelchair and lost the ability to talk naturally.

Sinfield has also followed the stories of rugby union players Steve Thompson and Alix Popham, who he knew from their time at Rhinos sister club Leeds Tykes and who are now suffering from early onset dementia.

However, he insists there should be no knee-jerk reactions to presuppose the sport endangers players' health without strong research.

"We need to do a lot more research on it," he said.

"As a club at the Rhinos we've invested into some mouthguard technology to do with concussion. I think it's really important that the whole area is researched properly and we get some answers rather than guess and try and make assumptions.

"It's really sad to see Steve Thompson, it's really sad to see Alix Popham, they both played up at Leeds Tykes, when they were our sister club, so I have spent some time with both of them in the past, and it's really tragic the story and the journey that both those players are on."

Asked if it was something which preoccupied his current players, Sinfield said: "I don't think so. It certainly wasn't in my mind as a player. You understand some of the risks to your body when you play.

"We need to do some research on it, we need to actually get the answers and make sure it's thorough so we can make the necessary adjustments, if any are needed."

Sinfield completed seven marathons in seven days to raise funds for the Motor Neurone Disease Association, and as of Monday afternoon the challenge had raised over £2.6million.

He says work is going on about how even more money can be raised next year, but it sounded as though a repeat of the marathon challenge was not on the cards.

"I think we will probably run with the 'seven in seven' theme, we'll get our heads together early in the new year and try and set something up," he said.

"I'm pretty sure it won't be doing seven marathons again. I'll certainly run some marathons for the MND Association but we'll look to do something different where hopefully, Covid-permitting, we can have a few more people involved and make it a really big fundraiser and awareness generator.

"As the week progressed during the seven marathons, the MND community fully got behind us. We understood that we were providing a little glimmer of hope, and it's really important for the whole MND community to let them know that people care.

"As you know, this only started out as a fundraiser for Rob and the MND Association, but what it's turned into has been much greater than that.

"We're all truly humbled and I can't thank people enough for their support and generosity in what has been a tough year for everybody."