Sudhakaran accused Sarin of betraying the party by leaving it just before the by-elections and contesting with the support of arch-rivals, the CPI-M.
He firmly asserted that Sarin would never be allowed entry into the Congress, even if he expressed interest in rejoining the party.
Sarin, who previously headed the IT wing of the Congress in the state, was expelled from the party after he rebelled against its leadership.
The revolt followed the nomination of Youth Congress Kerala State President Rahul Mamkoottathil as the UDF candidate for the Palakkad by-election.
Sarin blamed the candidate selection on the Leader of the Opposition, V. D. Satheesan, accusing him of undermining the party's interests in the state.
Days after Sarin's public criticism, the CPI-M welcomed and fielded him as their candidate against Mamkoottathil.
Sudhakaran also dismissed allegations from the Left Front that Congress candidate Rahul Mamkoottathil won the Palakkad by-election with the support of the SDPI, the political arm of the banned Islamist organisation - Popular Front of India.
"We never approached SDPI members seeking their votes, nor did any SDPI member contact us offering support in the polls. We did not ask any particular group to vote for our candidate," the Congress' Kerala unit President said.
He criticised the CPI-M for attempting to tarnish the UDF's image, claiming such efforts had failed.
Sudhakaran also reiterated his strong disapproval of Sarin's actions, describing his decision to join the CPI-M as a betrayal motivated by personal ambitions.
Regarding the Congress' loss in the Chelakkara by-election, Sudhakaran admitted the defeat was disappointing and announced that the party would review its election campaign strategies to identify shortcomings.
In the Chelakkara by-election, the Left Front candidate, U. R. Pradeep of the CPI-M, defeated Congress candidate Remya Haridas by a margin of 12,201 votes.
The election was necessitated after K. Radhakrishnan, the sitting MLA from the CPI-M, won the 2024 Lok Sabha elections from the Chevakkad Parliamentary constituency.