Published Friday, 06 September 2013
The south Belfast MLA and MP said it had been a tumultuous week for the party following Mr McDevitt's departure.
He dismissed claims there was ever any rift between him and the former MLA as "fantasy".
"Nobody was closer to me than Conall McDevitt," he said.
"Yes, there's always a degree of friendly competition in any constituency, and he was entitled to that. But we managed to take two seats out of south Belfast in the last election and we'll take two seats in the next election."
Mr McDevitt made the decision to step down with immediate effect on Wednesday after failing to declare a £6,750 payment he received in 2010 from PR company Weber Shandwick.
He had been the managing director of the company, but quit to move into politics and was chosen to succeed the SDLP's Carmel Hanna in the South Belfast constituency three years ago.
In an emotional interview with UTV, he said that stepping aside was "the most honourable thing to do".
He had made a tremendous impact; he was the runner up in the leadership contest two years ago and certainly Conall was seen as my successor.
On Friday, the SDLP leader admitted that he saw Mr McDevitt as his successor, as had many others.
"Conall was a very valued member of the assembly," Mr McDonnell added.
"His loss is a big loss to the party, we'll do our best to fill those shoes as quickly as possible."
Mr McDonnell said he had spoken to his colleague several times before his announcement but that "in the end it was Conall's own decision".
The party will be announcing nominees to replace Mr McDevitt's assembly role by Monday.
They are also due to name who will replace him at the upcoming Haass talks alongside Alex Attwood and on the Policing Board.
Mr McDonnell said that he had been working to rebuild the party, and that they had a "formidable" team of fresh councillors.
"We're moving into a serious political opportunity with the Haass talks, we want to see those talks succeed, we want to make sure that we maximise the SDLP contribution.
"We are going to ensure that we come out of the European election, and the local government elections next year, much much stronger than anybody gives us the credit for."
Mr McDonnell said that going forward, Mr McDevitt will be a "key player" in an advisory role.
© UTV News