Prime Minister Benjamin Netanyahu was undergoing medical assessments in an Israeli hospital on Saturday but was in good condition, his office said, with local media seeing no grounds for a handover of power.
Netanyahu, 73, was fully conscious en route to Sheba Hospital in Tel Hashomer, and walked into the emergency room, Israel's Channel 12 TV said, quoting the premier's doctor.
He was not undergoing sedation and no procedures were under way to declare him incapacitated, Channel 12 said.
Tel Hashomer is close to coastal Caesarea, where Netanyahu has a private residence. Israeli media said he was there when he reported feeling unwell.
Netanyahu took ill during the Jewish fast of Yom Kippur in early October and was briefly hospitalised. Israel has been in the grip of a weekend heatwave.
The veteran conservative leader is also in the eye of a political storm over his plan to overhaul the judiciary, which has set off unprecedented protests by Israelis worried for the future independence of the courts.
That has compounded tensions with the U.S. administration over his religious-nationalist coalition government's hardline tack on the Palestinians. In parallel, Netanyahu has been on trial in three corruption case in which he denies wrongdoing.
A brief statement from his office confirmed he was at Sheba and said he was in good condition undergoing medical assessment.