A source close to the detained lawyer said that he was growing frustrated over his inability to serve his constituents.
"He also realises the pressure he has put on his wife to work as his representative in the constituency in his absence," added the source.
His wife S Pushpaneela (right) has to juggle her time in taking care of their four young children, his legal office and his constituency as well, added the source.
Manoharan was detained under the ISA on Dec 13 in 2007 along with four other Hindraf leaders. He was a legal advisor for the movement, which has since been banned by the government.
He then contested under the DAP ticket for the Kota Alam Shah state seat in Selangor while under detention and defeated BN/Gerakan's Ching Su Chen by 7,184 votes. The state was also wrestled from Selangor by the Pakatan Rakyat alliance.
Various appeals to the government and judicial reviews at the courts to seek his release have been unsuccessful.
In his absence, Pushpaneela and several volunteers have been taking care of the constituency with the help of some DAP leaders.
"However the workload is just too much on her. She is after all not the elected representative and there is only so much she can do for the people," added the source.
Manoharan is now believed to have come to a decision that it would be better for someone else to do the job as an elected representative on Kota Alam Shah.
Wife meeting him on Saturday
When contacted, Pushpaneela refused to comment on the matter.
"I can't say anything until I have met him at the Kamunting detention centre this Saturday," she said.
"Please wait until Saturday for further information on this," she added.
If Manoharan steps down from the seat, it will pave the way for the seventh by-election in the country after the March 2008 general election.
As it is, a by-election is just around the corner - for the Penanti state seat in Penang, which will be held on May 31. That seat became vacant after its PKR's representative Mohammad Fairus Khairuddin quit on April 16.
The Kota Alam Shah by-election, if it happens, would be the first in Selangor and for DAP.
Pakatan has 36 seats in the state assembly as opposed to 20 held by Barisan Nasional.
The decision by Manoharan to step down, if it materialises, would surely cause a shock among the state leaders as this was one seat which they had not anticipated a by-election.
The state however came close to hold a by-election for the Bukit Lanjan state seat held by PKR's Elizabeth Wong after she got embroiled in a semi-nude photo scandal earlier this year but that did not materialise after Wong decided against resigning the seat.
Will BN contest?
A by-election in Kota Alam Shah would also put Barisan Nasional in a quandary as the coalition's chairperson and Prime Minister Najib Abdul Razak had recently lashed out at the opposition elected representatives for quitting their seats for flimsy reasons.
Najib had said that the nation was better off spending money on fighting the ongoing financial crisis than wasting it on by-elections.
It was in view of this that BN is contemplating of not contesting in the Penanti state seat. However a final decision is expected on Monday.
The coalition may take a similar view on Kota Alam Shah if the seat becomes vacant.
"But in the case of Manoharan, it is not that he does not want to serve his constituents. It is the decision of the government to hold him under detention, thus disabling him from performing his service," said the source.
"There is no way Najib can call Manoharan's reason to quit as being flimsy. He (Manoharan) is after all seems to be thinking for the benefit of his voters," added the source.
The Kota Alam Shah seat falls under the Klang constituency, also held by DAP.