"In the intelligence business, we would say that Mr. Putin has recruited Mr. Trump as an unwitting agent of the Russian Federation," Morell stated on Friday.
Morell said Putin's compliments of Trump play on the nominee's vulnerabilities.
Morell, who worked for both Democratic and Republican presidents during more than three decades at the CIA, said he supports Hillary Clinton for president.
"The character traits he [Trump] has exhibited during the primary season suggest he would be a poor, even dangerous, commander in chief,” Morell added.
The Kremlin has insisted that Putin has never had any contact with Trump or his staff either in person or over the phone.
Trump has repeatedly said Putin is a better leader than US President Barack Obama, and in June, said he would invite Putin to the United States if elected president.