Beck says hundreds of his unreleased songs may have been destroyed in a fire that swept through Universal Studios.
It is thought that more than 500,000 recordings were consumed by the blaze in 2008, with artists like Nirvana and Aretha Franklin among those affected.
The extent of the loss was not fully understood until the New York Times ran an exposé this June.
Beck says his management "still won't tell me what was lost", but he suspects the worst.
"I have a feeling that my management is not telling me because they can't bear to break the news," he told The Sydney Morning Herald.
One of rock's most prolific artists, Beck said up to 90% of his music remained unreleased, and could now be lost forever.
"An album like Sea Change, there are completely different versions of songs and then there's probably another 10 to 20 songs that aren't on the record that [were] in progress; things that I thought I would finish later," he said.
Several unreleased albums - including a double-disc set of Hank Williams covers, and a 10-track collaboration with Jon Spencer Blues Explosion - may also have been destroyed.
He added: "I went to Nashville on tour for two days and cut a country album that never got released. I have rock albums I did in the 1990s, before I did Odelay. But I don't know [what's gone], nobody's telling us anything. We didn't hear about it until the last year."
His comments echo those of Sheryl Crow, who said the master recordings of her first seven albums were destroyed by the 2008 fire.
"It absolutely grieves me," she told the BBC over the summer. "It feels a little apocalyptic.
"I can't understand, first and foremost, how you could store anything in a vault that didn't have sprinklers.
"Secondly, I can't understand how you could make safeties [back-up copies] and have them in the same vault.
"And thirdly, I can't understand how it's been 11 years," she added. "I mean, I don't understand the cover-up."
The fire, which took place in 2008, was started by overnight maintenance work. According to the New York Times, it claimed thousands of master tapes - the original recordings from which albums and singles are made - by some of the most famous names in music history, from Ray Charles and Chuck Berry to Janet Jackson and Eminem.
In the months since the publication of the Times article, Universal Music has stressed it is not withholding information about the lost music; saying it is still trying to gather information about the whereabouts of master tapes and any potential back-up copies.