Recent U.S. tax changes have weakened the case for companies like Pfizer (PFE.N) to shift their tax bases overseas by striking so-called tax inversion deals, according to AstraZeneca's (AZN.L) chief executive.

AstraZeneca fended off a $118 billion takeover bid from its larger U.S. rival in May but there is speculation Pfizer may return after Nov. 26, when it is allowed to make a fresh public offer under British takeover rules.

"The U.S. rules have certainly raised the bar for tax inversions for all companies that are considering tax inverting. They almost entirely remove the tax benefits," Pascal Soriot told reporters after presenting third-quarter results.

"It makes a tax inversion much less attractive."

He said he could not comment on how Pfizer would assess the situation, but pointed to the collapse of AbbVie's (ABBV.N) planned $55 billion acquisition of Shire (SHP.L) in another deal driven by tax considerations as showing the problems.

"It sends a very strong signal that the tax inversion risk is serious and has turned into a reality. It has cost AbbVie a lot of money and it has cost Shire a lot of distraction," he said.

Soriot declined to comment on whether he might be interested in moving to French drugmaker Sanofi (SASY.PA), which sacked its CEO last week. Many industry observers expect Sanofi's board to look for a Frenchman to take over. However, Soriot, who is a French citizen, said he saw himself as Australian, since his family was based there.