A defensive void at the Riverside Stadium has been created by the decision not to retain the services of Joszef Varga.
The Hungary international spent the 2013/14 campaign on loan in the North East, with the second half of the season seeing him provide cover at full-back.
The 26-year-old is, however, a holding midfielder by trade and the option to sign him permanently has not been taken up.
That has left Karanka with work to do in the transfer market, with the Spaniard aware of the need to get a specialist performer in before the new season starts.
He said in the Gazette: “It was not for me a surprise to play with Joszef as a right-back because I know him and I knew that he could play in that position.
“But, at the end of the season, it is better for both parties if we bring in another player.
“If we want success this season, we need the right players and I think it was worse for him than for us to get him again and play him at right-back again because he is a midfielder and I think he can have success as a midfielder.
“He’s a midfielder, not a right-back and I think we need a right-back.”