The club confirmed Idrizaj died at home in Austria.
A Swansea statement read: "We can confirm that the agent of young striker Besian Idrizaj has informed the club that the striker has sadly passed away.
"It is understood that the popular 22-year-old died in his sleep on Friday night while at home with his family in Austria."
The statement continued: "The exact cause of death has not been confirmed and our thoughts are with his family, friends and team-mates at this time."
Ex-Liverpool player Idrizaj spent three years at Liverpool after signing from LASK Linz in 2005 and was sold to FC Eilenburg three years later.
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Pay your tributes to Besian Idrizaj here
He joined Blackburn Rovers in the summer of 2009, but soon moved on to the Swans, debuting against Scunthorpe in the Carling Cup in August.
Idrizaj also had loan spells with Luton Town and Crystal Palace while at Liverpool, having been named Austria's Young Player of the Year before signing on at Anfield.
He went on to make three Championship appearances, two as a replacement, without scoring for the Swans and had a year left on his contract.
Idrizaj made no senior Liverpool appearances, but scored a 26-minute hat-trick at Wrexham for the Reds.
If confirmed as a heart-attack, Idrijaz's death follows several other similar deaths that have hit the sport in recent years.
In June 2003 Cameroon's Marc-Vivien Foe died aged 28 after collapsing on the field while playing against Colombia in Lyon, France having spent the previous season on loan from Olympique Lyon at Manchester City.
In August 2007 Spanish international Antonio Puerta, 22, suffered a heart attack playing for Sevilla against Getafe and later died in hospital.
Two years later Espanyol skipper Daneil Jarque died aged 26 after suffering cardiac arrest following a training session.
From BBC.
Rest in peace lad. You'll never walk alone.
