Bartomeu was thrust into the role of president on Thursday, after Sandro Rosell resigned his position amid reports Spanish courts are to open investigations into the transfer of Brazil international Neymar from Santos in the close-season.
The deal has faced claims of misappropriation of funds, with reports in Spanish daily El Mundo Deportivo alleging to have documents showing the cost of the Neymar deal was nearer to €95 million as opposed to the estimated figure of €57 million.
Barcelona took the unusual step of discussing the intricacies of the deal on Friday, after a confidentiality clause in the player's contract was lifted by Neymar's father.
There was confirmation that €40 million of the overall fee was paid to the company NandN, owned by Neymar's parents, though the player himself does not have a share in the organisation.
Bartomeu insists the club have not lied, adding that a lawsuit does not prove the club are in the wrong.
"Over the last few weeks there have been several issues, including the issue on Neymar," he said. "There will be questions about the contract. Until today we have treated it as a confidential contract so there will be several doubts.
"I assure you we will not be lying at any time, I guarantee we have not lied. As I said before, football games are won on the field of play not in the offices. We have always been highly responsible in the way we handle contracts.
"Here I have several of my colleagues. They are highly expertised in these matters. They know what they are doing.
"The member who placed the lawsuit has every right to do what he wants to do. Being named in a lawsuit does not mean you have done anything wrong."
Bartomeu also claimed Rosell's resignation was in part due to the fact he had received threats and not solely in response to the Neymar controversy.
He added: "(The focus on the Neymar deal is) not the only reason why Mr Rosell resigned. He has given his reasons. It wasn't only about Neymar. It was a security issue, he had threats against him. The Neymar issue is one of the causes, but not the only cause."
When asked why details of Neymar's contract had not been released before Rosell's resignation, Bartomeu stated the timing was coincidental and that no pressure had been applied to Neymar's father to make details public.
"Neymar's father only allowed us to do it (release details) in the last few hours," he continued. "The moment at which Mr Neymar has given us permission is nothing to do directly with Mr Rosell's decision yesterday.
"We have put no pressure on Neymar's father to lift the clause. He telephoned us today and said 'I can see serious things happening, if I am the problem go ahead and explain the full contract'.
"He contacted us and said he is willing for confidentiality to be lifted."
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