Speaking following the Spanish Grand Prix, the four-time world champion revealed the team could not match Mercedes' speed in the slow corners in the final sector in Barcelona, which is indicating an even tougher weekend in Monaco.
"It will be difficult for us because we are losing time in low-speed corners, we are struggling with those type of corners to put enough grip into the tyre and Monaco is all about that," Vettel said.
Mercedes recorded a best time in the final sector in Spain of 25.878s. Red Bull Racing were last year's winners in Monte Carlo, and their quickest was 26.322s, with Ferrari six-tenths back on 26.513s.
Vettel is pinning his hopes on the prestigious circuit being one where a driver can make a substantial difference, rather than the result being dependant on the car.
"It's Monaco, so the driver can make a difference," the German explained. "You need to have the right set-up and everything so there are a lot of things that in Monaco could be mixed."
Vettel has been victorious in Monaco twice in his career; once for Red Bull and once for Ferrari, in 2011 and 2017 respectively.