Italian oil and gas giant ENI may not have any investments in Iran, but its CEO Claudio Descalzi sees disruption ahead for oil markets thanks to the reimposition of U.S. sanctions on OPEC's third-largest oil producer.

"The impact is more for the crude oil price, because Iran now is exporting about 2.6 million barrels (per day), and if we go back to the first sanctions, they were exporting 1.5 million," Descalzi told CNBC's Hadley Gamble on the sidelines of the ADNOC Downstream Investment Forum in Abu Dhabi on Sunday.

When sanctions were imposed by the Barack Obama administration on Tehran in 2012, Iran's oil exports dropped to approximately 1.5 million barrels per day (bpd). Since the export restrictions were lifted in 2015, as part of the multilateral deal that offered economic relief in exchange for curbs to Iran's nuclear program — formally known as the Joint Comprehensive Plan of Action (JCPOA) — that figure increased by more than 1 million.

President Donald Trump announced on May 8 that the U.S. would leave the deal, immediately sending oil prices into a tailspin.

"So there is a lack of 1 million in the market and that is going to impact the oil price, and also the balance of different crudes," the CEO said. "Because 1 million is going to Europe, the rest to the Far East."

The vast majority of Iran's oil exports, more than 1.5 million bpd, goes to China, India, Japan and South Korea. Already Japan and South Korea have signaled they will try to seek waivers from the U.S. to continue buying Iranian crude.

"We have a demand that is increasing 1.6 to 1.7 million bpd yearly average, so that is going to create a disruption in terms of cost and price," he added. "And when we have this kind of situation, the landscape becomes very uncertain."

Some analysts, however, predict the impact will actually be minimal, particularly in comparison to Obama's 2012 sanctions — they say Trump could reduce Iran's oil shipments by 300,000 to 500,000 bpd, far short of the 1 million to 1.5 million bpd that were cut from the market six years ago.