Taysir Alluni's arrest came as a surprise to Aljazeera," Jihad Ballout, Aljazeera spokesman in Doha, Qatar, said.
"We are convinced that Alluni did no more or no less than pursuing his job in a professional manner.
"We have faith in the integrity of the Spanish legal system which we trust will ultimately acquit him of all charges," Ballout said on Friday.
Alluni's wife Fatima told Aljazeera that she was surprised that her husband had been arrested. She accused top Spanish judge Baltasar Garzon of making the case "a personal affair", and demanded her husband's release "because there is no new evidence" against him.
Fatima Alluni said she had no idea why the Spanish authorities should have arrested her husband again.
Alluni is known for his exclusive
reporting from Afghanistan
"They came to warn me so that I could bring him some of his things and his medicine, but I can't go to Madrid to be with him. I have a three-month-old child and I can't leave."
The Spanish authorities recently turned down a request by Alluni for accreditation to cover the first trial connected to the 11 March train attacks in Madrid in which 191 people died.
Alluni was re-arrested for his alleged links to the al-Qaida network, a Spanish judicial sources said in Madrid on Friday.
The decision to detain Alluni, a Spaniard of Syrian origin, was taken after a request by the Spanish prosecutor's office, which said there was a strong risk that he would try to flee the country before his trial.
He was due to appear before a magistrate on Friday who would then formally place him in detention, the source said.
"They arrested him in the evening [Thursday] at his office and police officers arrived to tell me this morning that they were taking him to Madrid at around 8:00am today," Fatima Alluni told AFP from her home in the southern city of Grenada.
"We have faith in the integrity of the Spanish legal system which we trust will ultimately acquit him of all charges"
Alluni was first arrested on 5 September 2003 in Grenada, where he lives with his family.
He is one of 41 people - including al-Qaida leader Usama bin Ladin - charged with links to, or membership of, the network and of using visits to Kabul to forge links with al-Qaida.
Suffering from a heart defect, he was released on bail in October 2003 but told he was not allowed to leave the country.
Aljazeera's Ballout pointed to the fact that the equivalent of a prosector-general in Spain had recommended to the courts that the case - at least for Alluni - be dropped in 2003.
Alluni found fame with exclusive reporting from Afghanistan during the US-led war on the Taliban launched in October 2001, interviewing bin Ladin and later reporting from Baghdad on the war in Iraq.
A date for his trial has not been set.