Portuguese Mourinho has had a testy  relationship with the Madrid-based media since joining from Inter Milan at the end of the 2009-10 season and declined to speak before a La Liga game against Barca in April, prompting a walkout by around 30 local journalists.
Barca coach Pep Guardiola is due to hold a news conference later on Friday.
Karanka noted he had given more than 30 news conferences since becoming Mourinho's assistant and refused to offer any explanation for the Portuguese's absence.
He told the packed press room at Real's Valdebebas training ground the club were treating Saturday's game like any other and there was no need to make any tactical changes given their recent impressive run of form.
"We tackle all our matches in the same way," the former Real player said, adding that their planned 4-3-3 formation would include Cristiano Ronaldo and Angel Di Maria on the wings and either Karim Benzema or Gonzalo Higuain at centre forward.
"Tomorrow's is just one more game," Karanka said. "Of course it's against a direct rival but that doesn't mean we have to change anything."
With roughly a third of the season played, leaders Real have a three-point lead and a game in hand over second-placed Barca, who are chasing a club record-equalling fourth consecutive domestic league title.
Real have won their last 10 La Liga matches, and their last 15 in all competitions, while Barca have lost only one of 11 Clasicos against their great rivals since Guardiola took the helm in 2008.
The former Barca and Spain midfielder has never lost at the Bernabeu as coach, boasting three wins and two draws with 13 goals scored and five conceded.
Mourinho has a full squad available except for Portugal centre-back Ricardo Carvalho, who is recovering from twisted knee ligaments and has not played since late September.
Guardiola also has a full roster, apart from long-term absentee Ibrahim Afellay, who is recovering from knee surgery in his native Netherlands.
Third-placed Valencia, four points behind Barca with a game in hand, need to pick themselves up for their game at struggling Real Betis after they were eliminated from the Champions League by Chelsea on Tuesday.
Captain Roberto Soldado said the club's goal now must be to steal second spot from Barca.
"We are playing very well in La Liga and that is where we have to find our motivation now," the striker told a news conference on Thursday.
Valencia's much smaller city neighbours Levante briefly topped the table in October for the first time but have slipped to fourth ahead of Saturday's game at home to fifth-placed Sevilla.
Sevilla's Ivory Coast striker Arouna Kone, who is on loan at Levante, said on Thursday he would not celebrate if he scored against the Andalusians and hoped to return there at the end of the season.
"Let's see if at the end of the campaign Sevilla want to sign me," he was quoted as saying in local media. "It will all depend on (their coach's) decision but it would be nice."
Erratic Atletico Madrid, in eighth, face a tough trip to Espanyol on Sunday following their 2-1 humbling at third-tier Albacete in Thursday's Copa del Rey last-32 first-leg match.
Coach Gregorio Manzano, who fielded a second string side for the Cup game, told reporters after the defeat he was not concerned about his job amid local media speculation he faces the sack unless Atletico's form improves.
Reuters