Alonso has been testing Ferrari's F138 car in Barcelona this week as part of the third and final winter testing event.
The Spanish driver told Sky Sports News: "I think we are a little bit behind the top teams, which is where we expected to be.
"In Brazil we were seven or eight tenths behind the Red Bull and McLarens and no-one can recover that amount of time in a couple of months.
"Hopefully we will arrive a little bit closer than that in Melbourne."
The 2013 season gets underway with the Australian Grand Prix on March 17.