The Uddhav Thackeray-led Maha Vikas Aghadi government of the Shiv Sena-Nationlist Congress Party-Congress alliance may face floor test in the assembly on Saturday, sources said.
The floor test is "most likely" to be held on Saturday, the Vidhan Bhawan sources said.
Governor B K Koshyari has asked Thackeray to prove majority by December 3.
Thackeray formally took charge of his office in Mumbai on Friday.
He took charge shortly after 2 pm, entering the sixth floor office of the CM, outside which a plate bearing the name 'Uddhav Balasaheb Thackeray' was put up.
When he reached Mantralaya, he paid floral tributes to the portrait of Chhatrapati Shivaji Maharaj in the building.
On way to Mantralaya from the Thackeray family residence Matoshree in suburban Bandra, he stopped at the Hutatma Chowk in south Mumbai and paid tributes to martyrs.
Thackeray, who is also the Shiv Sena president, was sworn-in as the chief minister on Thursday evening and presided over the first cabinet meeting on Thursday night.
Thackeray is heading the government of a three-party alliance, 'Maha Vikas Aghadi', whose main constituents are the Sena, the Nationlist Congress Party and the Congress.
Besides Thackeray, six other ministers -- two each from the Sena, the Congress and the NCP -- also took oath.