Ramzi Kassem, who has acted as a defence attorney for several detainees held at Guantanamo Bay, said it was "highly unusual" for a White House spokesperson "to say something that so clearly cuts against the principle of the presumption of innocence, which is at the heart of our judicial system."
"For someone like Mr Gibbs to come out so clearly against the presumption of innocence is egregious to say the least," he told Al Jazeera.
"This is what you get when you allow the politics of the moment to dictate your public statements."
Al Jazeera reports on the controversy over the the trial of the alleged 9/11 mastermind
Speaking to CNN, Gibbs did not confirm reports that the US administration had begun looking for places other than New York to prosecute Mohammed, and four other men accused of being co-conspirators of the 2001 attacks, in the face of criticism over security and costs.
"We are talking with the authorities in New York. We understand their logistical concerns," Gibbs said.
"We will work with them and come to a solution that we think will bring about justice."
Critics have said the government's plan to try the suspects just blocks from where the World Trade Centre stood before the 2001 attacks, would require a large security cordon, hurt businesses in the area and give the defendants certain legal rights in criminal court.
On Saturday, Dean Boyd, a US justice department spokesman, said: "We're considering our options."
The New York Times and the Washington Post newspapers have both reported that the lower Manhattan courthouse is out of the running for the trial, citing unnamed administration officials.
"Conversations have occurred with the administration to discuss contingency options should the possibility of a trial in lower Manhattan be foreclosed upon by congress or locally," an Obama administration official was quoted as saying.
|Gibbs said the White House was in talks with New York officials about the trial [Reuters]
It was not clear what other venues are under consideration.
Speaking to Fox News on Sunday, Democratic Senator Evan Bayh of Indiana said it would be hard to justify having the trials in New York because of the cost alone.
"I think this is one of those things that sounded good in theory, but in practice doesn't work so well," he said.
Al Jazeera's Washington correspondent John Terrett said originally New Yorkers and their mayor were behind the trial taking place there but over time they started to feel differently.
"Only last Wednesday Mayor Bloomberg said 'we don't want the trial'," he said.
"Now you have towns like Newburgh which is in New York upstate from the city saying they would like it because it would bring business into their area.
"They could choose many of the military bases around the city, such as the military academy of West Point, north of New York. My understanding is that it would still be a civilian court convened on the military base."
One White House official told the Reuters news agency that "no decision has been made" on the venue
Nearly 3,000 people were killed at the World Trade Centre in New York, the Pentagon in Virginia and in a field in Pennsylvania during the co-ordinated attacks.