Sheffield United defender and former Rotherham United & York City loanee Jack O'Connell announces his retirement at the age of 29

O'Connell, 29, a mainstay of the Blades side who achieved two promotions under Chris Wilder and reached the Premier League in 2018-19, suffered a serious knee injury in training in 2020.

Despite attempting a comeback, the Liverpudlian was never able to recover from the problem, with his last professional appearance coming on September 21, 2020.

His Blades deal expired in June and he was released at the end of the campaign.

O'Connell, who was tipped for England honours in the autumn of 2019, joined United from Brentford in the July 2016 and spent seven years at the club. He also had loan spells in Yorkshire at Rotherham United and York City.

Confirming his retirement on social media, he posted: "This is a very difficult announcement for me to make, although Sheffield United fans will already know that for the past three seasons, I have been fighting to save my professional career.

"Today, I am announcing my retirement from football.

"I have put my heart and soul into this recovery since my knee problems began in June 2020 but this is a battle I cannot win.

"The conditions that have forced me to make this decision and complex and there will be time to discuss them in more detail.

"For now, I would like to assure all Blades fans, and those who have supported me, that I gave it everything. Both in seeking expert medical advice and in following the rehabilitation programmes designed for me.

"There was a time in my career when I scarcely missed a game, I prided myself on my professionalism and my dedication.

"Even now, in terms of my cardio fitness and my general physique, I am as fit as I ever was when I was playing every week.

"Sadly, my body will not allow me to withstand the rigours of the game that I love."