Zardari told a Geo News TV host over the phone that no use of force would be undertaken against the marchers in Islamabad.
The clarification came when speculation was rife over the Pakistan government's next line of action to deal with the massive sit-in in the capital.
Qadri, a Pakistani-born Canadian cleric and Thehrik-e-Minhajul Quran leader, has been staging a protest along with his tens of thousands of supporters here since Tuesday to seek ouster of the government, dissolution of parliament and a corruption-free Pakistan.