The United States could have less than $50 billion in cash in mid-October when the government exhausts its legal borrowing capacity, Treasury Secretary Jack Lew said on Tuesday.
(Read more: What a government shutdown could mean)
Lew had previously said the government would have around $50 billion then. He said on Tuesday revenues have come in a little slower than expected in recent weeks.
"Because things have come in a little bit slower ... that number is smaller than 50 now," Lew told Bloomberg News in an interview in New York.
The government has been scraping up against its $16.7 trillion debt limit since May but has avoided defaulting on any of its bills by employing emergency measures to manage its cash, such as suspending investments in pension funds for federal workers.
The Obama administration has vowed not to negotiate with Congress over the debt ceiling, and Lew repeated the administration's call on lawmakers to allow the country to pay its bills.