Javier Hernandez has described his situation at Real Madrid as "frustrating" after playing 590 minutes for the club.
Luis Suarez refused to rule out a return to Liverpool and insists he will never play for another Premier League club.
Fitness assistant Carlos Cachada has arrived following stints in Turkey, Portugal and the Middle East.
Uruguayan goalkeeping coach Leo Percovich, who knows Karanka from their time together with Colorado Rapids, is also believed to be in line to feature as part of his staff.
The news comes as Boro have confirmed Mark Proctor and Stephen Pears have left the club as part of the re-shuffle following Karanka's appointment.
Karanka is expected to recruit further before the end of the month.
Meanwhile, chairman Steve Gibson has promised him funds will be available ready for the January transfer window.
"We're limited with transfer windows and we are limited by the availability of players," he said.
"We've talked about that (signings), of course, and that will be a developing situation.
"But we'll be doing everything possible to support Aitor."
Karanka is expected to tap into the Iberian markets, with his agent Jorge Mendes working closely with Gibson and Peter Kenyon - who is acting as an advisor to the Boro supremo.
Some players are expected to come in from Atletico Madrid's B side following a link-up between the two clubs was announced earlier this month.