Ferrari endured a difficult time during the 2014 campaign as they failed to win a single race and placed fourth in the constructors' championship.
Spaniard Alonso opted to end his five-season stay with the team in order to return to McLaren last month, after relations with Ferrari are reported to have soured.
The 2014 season was the first that the two-time world champion failed to claim a victory during his time with Ferrari, but he is confident that the vast resources at their disposal mean they will be serious challengers again in 2015.
"From the outside now it will be difficult to judge how Ferrari is doing, but they have the talented people, they have the resources, they have the motivation from everybody in the team, so in time they will win," Alonso said.
"I think what they missed these five years is just some more performance in the car, and technical resources.
"They have not been at the top level sometimes in the aspects of the car, in some of the aerodynamics in the beginning, and some of the power unit now.
"[But with] the budget they have, next year they will be favourites, because every season the favourites at the start will be Ferrari.
"They must be, everyone is expecting Ferrari to win in Formula 1. Next year they will be very strong."