The Spaniard said that there are "exciting times" for Boro fans now that his compatriot is at the helm, but urged them to give him time to reverse the team's fortunes.
"It is a new start and a statement from the club in the direction that they want to go and it is exciting times for Middlesbrough fans, and could be exciting times over the next few years," he told Sky Sports News.
"I don't think [Jose] Mourinho would recommend anyone he didn't think was capable of doing a job.
"At the moment it is a club set up for a different manager so I am sure he will have to make changes as soon as he can, probably the real idea of the real Aitor Karanka will be next season when he has control of new players and those leaving and will be in charge of how they are playing."
Karanka's first game in charge will be the visit to Leeds United on November 23.