Plaid Cymru must rebuild around a single leader after suffering two blows in the general election, according to former MP Simon Thomas.
Simon Thomas was beaten by 219 votes in Ceredigion
As well as Mr Thomas losing Ceredigion, Plaid also failed to win its main target seat of Anglesey in the polls.
Plaid's leadership team are meeting on Monday to discuss the party's future.
The party is currently jointly led by president Dafydd Iwan, Parliamentary leader Elfyn Llwyd and Welsh assembly leader Ieuan Wyn Jones.
Mr Thomas, Plaid's policy director, said he had not been expecting his defeat by Liberal Democrat Mark Williams.
"I was getting a very positive response on the doorstep and that's one of the really frightening things about this loss," he said.
"I think we have questions to ask about the leadership and also about our strategy.
"I think we do need an identifiable leader around which the party coalesces and around which the people of Wales can identify and see as a putative first minister.
"Realsitically that person has to be in the assembly."
The system of having three leaders arose when Ieuan Wyn Jones, who was Plaid's president and its leader in the Welsh assembly, resigned after the 2003 assembly elections, in which Plaid lost five of its 17 seats.
Mr Jones then recontested and won the assembly leadership, with Mr Iwan becoming the party president.
"I think we can see that this strategy simply isn't working for us," said Mr Thomas.
Dafydd Iwan and Ieuan Wyn Jones are two of Plaid's three leaders
"I think the party needs to rebuild and I think the party needs to see by 2007 that single person around which they can identify in the assembly as the person who has the potential...to unite - not just Plaid Cymru members but also build a broader coalition," he said.
Mr Thomas, who backed AM Helen Mary Jones in her bid to become the party's assembly leader, said that he did not want to talk about personalities at this stage.
"I think this is where Plaid Cymru has to be extremely hard-headed, and not take into account some of the personalitites involved and the feelings of personalities," he said.
"I don't think we are going to get any electoral success in Wales unless we are clearly identified in a modern televisual age with one leader."
He added that he did not know what he personally was going to do in the future, but was looking forward to "a couple of months with the family".