The 25-year-old has found game time hard to come by this season, managing to see just 341 minutes of La Liga action so far in 2014-15.
Schalke are reportedly interested in the central defender as they look to cover the injured Benedikt Howedes.
However, Fernandez insisted Barcelona will not be letting Bartra go anywhere.
"We will not let him leave," he told Movistar+. "We are quite sure of that."
Meanwhile, Fernandez said he would not stop Douglas leaving in search of more game time.
The 25-year-old full-back has appeared just three times in La Liga since his €4million move from Brazilian outfit Sao Paulo in 2014.
"We will see if something beneficial comes along for the player and the club," Fernandez said.
"We'd like him to be playing."