Spencer came through the youth system at Sunderland before joining Leeds United. He left Elland Road for Derby County last summer, but has now been forced into retirement.
"Heartbroken to be saying this," the 21 year-old posted to Instagram. "I will be retiring from professional football due to a cardiac problem I can't carry on with. All I've ever known is to kick a ball and I have learnt everything from the game.
"I'm thankful and proud of what I have achieved. I will never forget the memories I have and have created along an amazing journey. Football is in my DNA and I will continue to support everyone who helped me along the way.
"I want to thank everyone who has stuck with me during this tough period and everyone who has helped me during my career."
Spencer's retirement comes just weeks after Irish youngster Ben Dumigan was also forced to hang up the boots due to heart issues.
Dumigan was due to complete a dream move from Cork City to Hoffenheim in January when a problem was spotted during his medical.
He was diagnosed with hypertrophic cardiomyopathy, which causes abnormal thickening of the heart muscle.