"It's sad for all the Swansea family, but more importantly his own close family. Our whole-hearted condolences go out to them."
Idrizaj died in his sleep while at home with his family in Austria. The exact cause of death has not been established but a heart attack is suspected.
"He was a player I had every faith in," said Sousa.
He was fighting hard to fulfil his dream and it's difficult to comprehend why that's been taken away from him at such a young age
Paulo Sousa
"He worked hard throughout the season to get stronger and back to his best and I think by the end of the season all his team-mates could see what a talented boy he was.
"He was growing and getting better and stronger all the time and I fully expected him to show that talent to everyone in the Championship next season on a regular basis.
"He was fighting hard to fulfil his dream and it's difficult to comprehend why that's been taken away from him at such a young age.
"The only saving grace is that he didn't suffer and he was close to the love of his family at the 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.
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.
Source: BBC Sport
Source: BBC Sport