Portuguese goalkeeper Hilario will complete his move to Chelsea after his medical at the club on Thursday.
Hilario has worked under Jose Mourinho at Porto
The 30-year-old is expected to sign a two-year deal from Nacional, according to reports in Portugal.
He will become boss Jose Mourinho's third-choice goalkeeper behind Petr Cech and Italy's Carlo Cudicini.
Hilario said: "I feel privileged to be a part of this giant club and I have come here with two aims, to work hard and to make it difficult for Mourinho."
He added: "I want to complicate his life. There are many minutes in a season and I am going to work hard in order to earn the confidence of the coach."
I already worked with him and I know he is intelligent
"I respect and admire Cech and Cudicini, they are two great goalkeepers."
Hilario played under Mourinho at Porto in the 2003/04 season.
And Mourinho told Portuguese TV on Wednesday: "I already worked with him and I know he is intelligent.
"It's necessary to be intelligent in order be a substitute to the best goalkeeper in the world.
"He is not only bright but he also has common sense."