The 24-year-old has scored 10 goals and registered nine assists in 34 appearances for the Blues since his arrival last summer but just five of those strikes have come in the Premier League.
Werner drew another blank in Chelsea's 1-0 win over Atletico Madrid in the Champions League on Tuesday night, and Ferdinand criticised the Germany international's overall contribution against the Spanish club.
"It's frustrating watching him, because you've seen clips of what he can do," Ferdinand told BT Sport. "He gets into these areas, makes the keeper make a save, fair enough, but there's far too many times when he's loose in possession when building up, or decision making when he gets into these areas at times.
"Sometimes fast players have to slow the game down a bit. They're running so fast everything seems to be a blur."
Werner has only scored once in the Premier League since the start of November, while he has not registered in his last four Champions League appearances for Thomas Tuchel's side.