Ali Dursun and Hasan Cetinkaya, who also represent Barcelona striker Martin Braithwaite, flew into the city on Wednesday and are expected to hold talks with the Catalan club in the coming days over both of their clients.
De Jong's future has been the subject of much attention throughout the summer. ESPN revealed in July that Barca had agreed a fee of around €85 million with United, including add-ons, while Chelsea are also interested.
However, the player has so far preferred to remain at Camp Nou.
Barca, meanwhile, have told De Jong that if he wants to stay, he must reduce his salary, although sources have told ESPN he is reluctant to do so at this stage.
Sources confirmed to ESPN earlier this week that Barca sent a letter to De Jong's camp in July warning that the contract renewal he signed in 2020 under the previous board had alleged irregularities.
Sources close to the player said the contract is legal and claim the letter that Barca sent was intended to put pressure on De Jong to either accept a move away or agree a wage reduction.
However, the timing of Barca's tactics has drawn questions as they try to raise funds and reduce their wage bill to be able to register their summer signings.
Still, the uneasy situation was highlighted when De Jong arrived at training on Wednesday and was subjected to shouted abuse by some Barcelona fans, who called on him to accept a reduced salary.
Dursun and Cetinkaya also represent Braithwaite, who has been told by Barca to find a new club. The Denmark striker was left out of the squad for the tour of the United States last month and has not featured in preseason.
Braithwaite, 31, was even jeered by Barca supporters before Sunday's game against Pumas. Sources have told ESPN he is open to leaving the club, who he joined as an emergency signing from Leganes for €20m in 2020, but only if the offer is right for him.
Meanwhile, Barca continue to negotiate further wage adjustments with Pique and Sergio Busquets. Sources have said talks have gone well so far.
With Barca set to kick off the new LaLiga season on Saturday against Rayo Vallecano, none of their five signings have been registered with the Spanish league, nor have the new contracts signed by Ousmane Dembele and Sergi Roberto.
The club have so far sold assets worth over €600m and are now in a position to register some of their signings. However, a league source told ESPN more money must be raised -- or wages cut -- before Saturday to register everyone.