Both of those aforementioned clubs have been linked with the £30 million-rated midfielder in recent times, with Koke having played a starring role for Los Rojiblancos during their fairytale rise to the La Liga title last season.
The 22-year-old playmaker is currently in Brazil as a member of Spain's final 23-man squad for the World Cup and in an interview that was quoted by The Daily Express, he appeared keen to ensure that people were aware of his plans for the future so that he isn't distracted from his goal of helping Vicente del Bosque's men to successfully defend the trophy they won in South Africa four years ago.
"My future is with Atletico. I am happy in my club and now I have a deal and do not think about an exit," he said.
"Really my head is only focused on the work for Spain in Brazil 2014."
To hear Koke re-affirm his commitment to Atletico in such certain terms will come as a considerable disappointment to his suitors.
As new Manchester United boss Louis van Gaal and executive vice-chairman Ed Woodward frantically search for potential new recruits this summer, Koke would have been a fantastic upgrade over the likes of Tom Cleverley at Old Trafford and would surely have quickly cemented a reputation as one of the club's most important players.
A sublime passer with strong instincts and incredible vision, it is difficult to overstate the sort of impact that the Madrid-born midfielder may have had in the Premier League.
Barcelona will be well aware of his qualities of course, with the Catalans having been bested by Atletico both domestically and in the Champions League during an astonishing 2013/14 campaign that will live long in the memory.
As new head coach Luis Enrique takes the reins from Gerardo Martino at the Nou Camp, Koke may well have been viewed as a gifted long-term successor and rightful heir to Xavi as he approaches the end of a stunning career in which he has established himself as one of the most important players in the history of both Barcelona and Spain.
While Koke's comments will serve as a negative for Manchester United and Barcelona, however, Atletico supporters should be hugely boosted by such a positive outcome.
The club are certainly entitled to expect a hint of loyalty from the player considering he was only awarded a new contract at the Vicente Calderon, but such an emphatic statement should raise a few smiles nonetheless.
During a summer where Atletico are expected to be stripped of the majority of their prized assets in Diego Costa and Filipe Luis as well as possibly the likes of Miranda, Arda Turan and Chelsea loanee Thibaut Courtous, the fact that one of their brightest stars seems so committed to staying put gives them at least a fighting chance of competing for honours once again next season.