The Barcelona president claimed he was not surprised by the Argentine's two-goal display at Sevilla but said talks over a new deal for the 26-year-old are not imminent.
Along with the rest of his teammates, Messi performed poorly in last weekend's 3-2 defeat at home to Valencia, leading former Barca assistant Angel Cappa to claim the Argentine had lost his passion for the game.
However, the 26-year-old hit back in some style with two great goals in wet and windy conditions Sunday as Barcelona beat Sevilla 4-1 at the Sanchez Pizjuan.
"We were not worried," Bartomeu said of Messi. "Everyone is entitled to their opinion, [but] we are closer to him than the people who are writing or talking.
"He makes the difference and he showed that yesterday in very difficult conditions."
However, the new president claims there are no talks planned at the moment to improve the Argentine's current contract at the Catalan club.
"Leo has a contract," he said. "He is the best player in the world and we want him to be the highest-paid player in the world. When the moment is right, we will look at it [his renewal].
"At the moment, however, we are focused on the [three] competitions, so it's not the time to talk about that."
Also asked about a possible new contract for coach Gerardo Martino, Bartomeu gave a similar response.
"He is doing a magnificent job," the president said. "Now is not the time to negotiate, but we are delighted with his work."
Barca takes a 2-0 lead to Real Sociedad on Wednesday as the two sides meet in the second leg of their Copa del Rey semi-final, while the Catalans face Manchester City in the last 16 of the Champions League later this month and currently lead La Liga on goal difference from both Real Madrid and Atletico.