United have tabled a bid for the former Arsenal midfielder as David Moyes looks to lure him back to the Premier League.
The Red Devils have made Fabregas one of their top targets this summer as they aim to add some creativity to their midfield.
Moyes revealed earlier on Friday that he was waiting to hear soon on the club's bid for Fabregas as he tries to make his first big-name signing at Old Trafford.
However, Bartomeu has moved to quell any talk of an imminent transfer for Fabregas by insisting they will not entertain any offers for the Spain international.
"Barcelona can assure you we will not entertain any offers for Cesc," Bartomeu was quoted by Spanish daily Sport. "It is totally ruled out, he's not for sale."
Fabregas has always repeatedly said he wants to stay at his hometown club and it appears Barcelona have no plans to lose the 26-year-old this summer.
The player's stance was reiterated by Barca boss Tito Vilanova on Tuesday as he said: "It's normal to receive offers for our players from other teams. We have very good players, and we have to be very happy to have Cesc with us.
"I am conscious that he has received offers for other teams, but I had a conversation with him and he let me know that we wanted to stay here, and his dream is to be successful here.
"So he is not thinking about any other club, not even for money or for minutes, even if he knows all the competition he has here with Xavi, Iniesta and also this year against Sergi and Roberto, but he told me that his dream is to be here. I'm not worried at all."
Regarding the offer for Fabregas, Moyes had said: "I couldn't tell you exactly where we are with that, but I will hopefully know a little bit more in the next day.
"I might have a little bit more information about how it's going."
Chief executive Ed Woodward left United's pre-season tour ahead of schedule on Wednesday in order to return to Europe to carry out urgent transfer business, with it understood to concern a player arriving at Old Trafford.
He was due to return home on Sunday and his decision to cut short his trip to the Far East indicates the urgency of the situation requiring his attention.
Red Devils goalkeeper David de Gea, meanwhile, would welcome Fabregas at Old Trafford.
He told the Daily Mail: "He is a great player, very skilful, knows how to win things and you always want those type of players in your team."