"The Berlin prosecutor's office is examining the legal assistance request" from Egypt, he added.
Dual Egyptian-British national Mansour is to appear Monday before a judge, who is to decide whether to keep him in detention and launch extradition procedures or release him, one of his lawyers, Fazli Altin, told reporters.
An Egyptian court sentenced Mansour in absentia in 2014 to 15 years in prison, for "torturing a lawyer in 2011 on Tahrir Square" in Cairo, epicentre of an anti-regime uprising that brought down former president Hosni Mubarak.
The 52-year-old journalist told Al-Jazeera he rejected the "absurd" accusations, adding that he was facing rape, kidnapping and robbery charges -- accusations which he also denied.
Ties between Doha and Cairo have been extremely strained over Qatar's backing for the former, short-lived Egyptian government under the Muslim Brotherhood.
Three Al-Jazeera journalists, including Australia's Peter Greste and Canada's Mohamed Fahmy, were arrested in Cairo in 2013 and sentenced to up to 10 years in prison on charges of supporting the Muslim Brotherhood.
Greste has since been deported while the other two are facing a retrial.
In a video aired by the Doha-based pan-Arab satellite channel, Mansour strongly criticised Berlin.
"The coup regime in Egypt is too weak to drag a state like Germany and the EU into its dirty game against Egyptians," said Mansour, referring to the Egyptian military's ouster of Islamist president Mohamed Morsi in July 2013.
Mansour also said he had been told by police that his arrest was "based on a German order, and not due to an Interpol order."
He tweeted in detention on Saturday that Berlin was colluding with Cairo.
"The question now is how have the German government and Interpol become tools in the hands of a bloodthirsty regime in Egypt that came to power through a coup, and is led by the terrorist Abdel Fattah al-Sisi."
Interpol confirmed to AFP that it had not issued a "red notice", an alert notifying that a person is wanted in a member country, against Mansour but declined further comment on the case.
- 'Cairo's capricious regime' -
About 70 protesters gathered outside the jail in central Berlin where Mansour was being held, demanding his release.
The group calling itself the German-Egyptian Union for Democracy held up placards reading "Freedom for Journalist Ahmed Mansour" and "The Legitimate President of Egypt" with an image of Morsi.
Another lawyer for Mansour, Patrick Teubner, said Mansour was "doing well under the circumstances."
"He is very composed. He assumes and he knows it's politically motivated and he trusts that it will be dealt with correctly here," Teubner said.
German opposition politicians also sharply criticised the arrest.
"Berlin justice authorities must under no circumstances allow themselves to become the agents of Cairo's capricious regime," a deputy from the Greens party, Franziska Brantner, said in a statement.
"Germany must not extradite him."
The deputy parliamentary group head of the far-left Linke party, Wolfgang Gehrcke, told Cologne's daily Stadt-Anzeiger that the rule of law in Egypt was "fragile -- if you can even speak of the rule of law."
Mansour, who hosts a popular news programme, recently interviewed Abu Mohamed al-Jolani, the chief of Al-Qaeda's Syria affiliate, Al-Nusra Front.
While in Berlin, he interviewed an expert on Islamist militants from a prominent German think-tank.
His arrest comes on the heels of a visit by Sisi to Germany on June 3.
Rights groups had urged Chancellor Angela Merkel to press him to end grave rights abuses.
At a joint press conference with Sisi, Merkel voiced criticism of Egypt's use of the death penalty and record on religious freedom, but pledged closer economic ties with its partner in the fight against Islamic extremism.