Garfunkel was due to perform as part of a touring concert entitled "Night of the Proms" alongside Anastacia, Måns Zelmerlöw and John Miles, but shortly before he was due on stage the veteran crooner disappeared.
Julius Malmström confirmed that he had last seen Garfunkel when they drove around in Gothenburg on Thursday, revealing that the artist had expressed concern over his voice.
"He seemed fit but not completely happy with his voice. It is possible that he was off colour, but if you are sick then you need to go to the doctor and get a certificate for your employer," he told the newspaper.
"This is bad form. Not least for himself. He is an icon in the business and it is regrettable if his career will end like this."
Malmström explained that ticker-holders would be entitled to a partial refund once he had contacted Garfunkel's US management on Monday to ascertain what had happened and why Garfunkel had decided to return home.