According to BBC, John Brennan also advised the new president to be wary of Russia's promises, blaming Moscow for much of the suffering in Syria.
In his campaign, Mr Trump threatened to scrap the Iran deal and also hinted at working more closely with Russia.
Mr Brennan will step down in January after four years leading the CIA. BBC reports.
In the first interview by a CIA director with the British media, John Brennan outlined a number of areas where he said the new administration needed to act with "prudence and discipline" - these included the language used regarding terrorism, relations with Russia, the Iran nuclear deal and the way in which the CIA's own covert capabilities were employed.