Mr Hichilema is accused of obstructing the motorcade of President Edgar Lungu when it was travelling to a traditional ceremony at the weekend.
Mr Hichilema's UPND party has in the past accused the government of trying to stifle all dissent.
Last year, President Lungu narrowly beat Mr Hichilema in the presidential election.
The UPND is challenging the result of the vote.
The opposition leader's lawyer Jack Mwiimbu told the BBC Focus on Africa radio that Mr Hichilema denies any wrong-doing.
He added that his client had not been formally charged.
The authorities have not commented on the politician's detention.
Mr Hichilema was detained after armed police raided his family home, during which teargas canisters were thrown inside.
His lawyer questioned why only Mr Hichilema was being held despite him having been in a convoy of more than 60 cars when the incident happened.
Mr Mwiimbu said his client was being detained "based on treasonable charges under the laws of Zambia" and had therefore been denied bail.
Mr Hichilema is already facing charges of sedition dating from last October; a move his team said was an attempt by the ruling party to silence dissent.