The popular left-back requires back surgery to correct a lifelong problem. The 22 year-old also revealed that he had a minor heart operation in the summer which caused him to miss the entire pre-season programme.

Day will have an operation to cure a displaced vertebrae in three weeks. He will be out of action for between six and nine months.

Day said: "I'm devastated to be honest. I'm determined to stay positive, but it's not easy. I've known something was wrong since I started training.

"I was struggling through the training sessions and grinding my way through matches. It was painful, but I was kidding myself that there was nothing wrong and that it would go away.

"But it never got any easier and it was clearly affecting my performances. I won't use it as an excuse because I made myself available to play, but it was a struggle.

"In the end I had to accept something was wrong and I've seen a couple of specialists who have told me the same thing.

"The problem is something I've had since birth, but the surgeon reckons he has had great success with similar operations so I should come back okay.

"It's hard to accept the season is over for me already, especially as I have just enjoyed my best ever-season, but I have some good people around me and that will help.

"The rest of the players and the manager have been great and the chairman has already been on the phone offering his support.

"I just want to get the operation over with and get fit again. The heart complaint was also something that has been with me since birth and I was suffering a bit in the summer, but that particular problem has been cured."

Day was one of the stars of last season. He played 42 of the 46 League Two matches as Posh secured promotion.

Posh manager Darren Ferguson said: "It's a terrible blow for the lad. He's not just a very good footballer, he's a top bloke so it's disappointing for him and everyone who knows him. It's typical of him that he wanted to carry on playing through the pain.

"He was one of our best players last season and I am convinced he would have been a success again in League One.

"He's had terrible luck what with his heart trouble and now this, but I am sure he will come back as strong as ever."

Day has played just five games this season.