Congress president Sonia Gandhi Sunday cancelled her day-long tour of Maharashtra, citing health reasons.
She was to address three election rallies in the state -- first in Dhule, followed by Nandurbar and Mumbai.
Congress sources said Sonia Gandhi was unwell, but refused to disclose any details.
Party vice president Rahul Gandhi, along with Nationalist Congress Party chief Sharad Pawar, addressed the Mumbai rally.
Actor-politician Raj Babbar and union Health Minister Ghulam Nabi Azad addressed the other rallies on her behalf, Congress sources said.
Sonia Gandhi was to address the poll campaign ahead of Thursday's election in Mumbai, which is part of the 19 constituencies going to polls April 24 in the third phase in the state.
Bharatiya Janata Party's prime ministerial candidate Narendra Modi has already addressed a rally in Mumbai.
Modi will Monday address a rally at the MMRDA ground at the Bandra-Kurla complex, where Sonia Gandhi was scheduled to take the dais Sunday.
In 2011, Sonia Gandhi had suddenly flown off to the US for surgery for an undisclosed ailment.
Rahul Gandhi, addressing the MMRDA ground rally, attacked Modi and said the Gujarat chief minister would have even "ousted" former prime minister Atal Bihari Vajpayee like he has party veterans Jaswant Singh and L.K. Advani.