Cook, speaking in an interview with CBS News that aired on Tuesday, said Apple controlled a moderate share of the market but was not too big, and disagreed with calls from some US politicians that the company be broken up.
"With size, I think scrutiny is fair. I think we should be scrutinised," he said. But, he added, "I don't think anybody reasonable is gonna come to the conclusion that Apple's a monopoly."
On Monday, sources told Reuters said US authorities were preparing to launch what could be a wide-ranging probe with oversight divided between the Federal Trade Commissionand the Department of Justice. US officials must still decide whether to open formal investigations.
Shares of Apple and other tech giants - Facebook, Google owner Alphabet and Amazon.com - fell on Monday following news of the probe. Their shares were all up slightly in premarket trading on Tuesday.
Technology companies have faced increased scrutiny on a range of issues from privacy and their impact in the 2016 election to advertising and their effect on the marketplace.
US President Donald Trump has urged closer examination of social media companies and Google, accusing them - without offering evidence - of suppressing conservative voices online.
He has also repeatedly slammed Amazon, whose CEO, Jeff Bezos, owns The Washington Post, another target of Trump's ire over its news coverage of him and his administration.
Congress has weighed in with hearings on big tech. Both Republican and Democratic lawmakers on Monday welcomed potential federal investigations.
Reuters