Deora said that he had supported Matondkar "wholeheartedly" during Lok Sabha election campaigning. "After Urmila Matondkar decided to fight LS elections from Mumbai North, I supported her campaign wholeheartedly as Mumbai Congress president."
Deora said he stood by her "when she was let down by those who brought her into the party".
"Fully agree that Mumbai North leaders MUST be held accountable!" he tweeted.
Earlier in the day, Sanjay Nirupam took to Twitter to say that infighting was "part and parcel of every organisation" and urged Matondkar to reconsider her decision to quit the party.
"We must fight against this instead of giving up. I had cautioned Urmila Matondkar long ago and told her not to get into it and have patience. It's unfortunate that she has resigned. Request her to think over her decision," he said.
In a statement, Matondkar said "It is obvious that the key functionaries of Mumbai Congress are either unable or not committed to bringing about a change and transformation in the organisation for the betterment of the party. My political and social sensibilities refuse to allow vested interests in the party to use me as a means to fight petty in-house politics instead of working on a bigger goal in Mumbai Congress."
In July this year, her letter to Deora, the then Mumbai Congress chief, mentioning discrepancies at the local level in the party went viral on social media.
Matondkar had lost to BJP leader Gopal Shetty by 4,65,000 votes.