Rabbi Ovadia Yosef, 92, is conscious and in a stable condition, Hadassah hospital spokeswoman Etti Dvir said, adding that doctors had requested he remain in the facility for several days for observation and further checks. She did not provide further details on his ailment.
The enigmatic, Baghdad-born Yosef is the chief spiritual adviser of the Shas party, which represents Israeli Jews of Middle Eastern descent. His followers consider his decisions as binding religious law—rare discipline in Israel's otherwise fragmented political landscape.
Israeli media reported he was rushed to Hadassah hospital after collapsing during morning prayers in a synagogue on Saturday morning.
Dr. Yuval Weiss of Hadassah told reporters Saturday night that the rabbi "likely had a very mild stroke."
"He is conscious and fully communicating with those around him," Weiss said. "I hope he can return home in a few days," he said.
Yosef's influence reaches beyond the party, which holds 10 seats in the 120-seat Israeli parliament. Comments from the rabbi, with his trademark turban, gold-embroidered robes and dark glasses, have cast a pall over political debates ranging from whether ultra-Orthodox Jews should be conscripted into Israel's military, to war and peace with Palestinians.
He is known for his fierce statements that have offended widely disparate segments of society, including Holocaust survivors, gays, Palestinians and secular Jews.
The rabbi said during a sermon in August 2010 that Palestinian President Mahmoud Abbas should "perish from the world" and described Palestinians as "evil, bitter enemies of Israel." He later apologized for the remarks.
In 2007, he said that Israeli soldiers died in battle because they were not religious enough and said the victims of Hurricane Katrina in the U.S. suffered "because they have no God."
In 2008, Shas under his direction forced new elections by refusing to remain in the government after then-prime minister Ehud Olmert resigned.
Olmert's successor, Tzipi Livni, was unable to preserve a governing coalition because Yosef insisted she commit to not discussing the future of Jerusalem in expected peace talks with Palestinians.
Politicians from outside Yosef's party often lobby for his support on tough decisions, including whether to target arch-foe Iran.
Despite his often hawkish stances, Yosef has signaled he would support Israel's withdrawal from the West Bank, a territory Palestinians seek for their future state, if it saves lives.
Shas was predicted to recoup its seats when Israelis vote later in January, but the party's fortunes are unclear if Yosef remains hospitalized.
The rabbi is literally the face of Shas: On the main entrance to Jerusalem, Yosef's face is draped over a large building, urging people to vote for the ultra-Orthodox party, saying they will remember the poor.
Yosef has been hospitalized with heart problems in the past.
Shas party members were unavailable for comment because it is the Jewish Sabbath, when the devout refrain from non-lifesaving work.
Yosef is a highly respected religious scholar, often called the outstanding rabbinical authority of the century from the Sephardic tradition, that of Jews from Arabic-speaking and other Middle Eastern nations.
His insistence that Sephardic tradition is as valid as the European Ashkenazi version of Judaism spawned a religious and cultural awakening among Jews of Middle Eastern, or Mizrahi, background.
He used that influence to transform the Mizrahi Jews from a downtrodden community of immigrants into a proud, powerful force in Israeli politics. Jews who descend from Arabic-speaking countries make up nearly half of Israel's Jewish population.
Yosef came to national prominence when he served as Israel's chief Sephardic rabbi from 1972 to 1983.
Born in the Iraqi capital in 1920, Yosef was four years old when his family moved to Jerusalem.