Barca's midfield has deteriorated in recent seasons, with the exit of club legend Xavi and Andres Iniesta's advanced age causing the Catalan club to bring in reinforcements, few of which have lived up to expectations.
Andre Gomes in particular has come in for serious criticism since his move from Valencia in 2016, prompting the Blaugrana to continue their search for improvements in the middle of the pitch.
Barca ultimately signed Paulinho this term, with the Brazilian surprising many by settling in wonderfully at Camp Nou, but the former Tottenham man was not the club's first choice according to Marin.
"Bartomeu called me in the summer to tell me they needed a player of Saul Niguez's characteristics and that they intended to pay his release clause," the Atletico supremo told Onda Cero.
"What he didn't know was that, three days beforehand, we had signed a new contract and his clause went up from 80 to €150million."
On the subject of potential exits from Atletico, another player to be linked with a move away is Yannick Carrasco, with Premier League champions Chelsea among those linked with a January bid for the winger.
It has been claimed the Belgian has fallen out with some of his team-mates and the coaching staff, prompting Diego Simeone to sanction his departure, but Marin is adamant that is not the case.
"The idea with Carrasco is that he stays and is one of our major reinforcements for the winter," he said, "People talk because, without knowing anything, it's easy to do so.
"He had problems with his knee and that's the reason why he hasn't had a good first half of the season."