"If [Red Bull] can start, go away and have an easy race, that's the worst news for us," Alonso said.
"Tomorrow we need to overtake McLaren as soon as possible and put pressure on Red Bull. We are not only fighting against Sebastian, but also against [technical director Adrian] Newey, they have finished first or second in the last four races.
"It's not an easy fight, especially on a Saturday but on Sunday we are usually more competitive."
Alonso will start alongside his teammate Felipe Massa, who qualified sixth.