The Boro squad has been boosted further since the club's last outing, a 0-0 draw at West Brom, with Calum Chambers having arrived on a season-long loan deal from Arsenal and Adama Traore on a permanent move from Aston Villa, completing an overhaul which has given Karanka a range of options.
Karanka said: "It's my job and it's the most difficult thing, to try to have all of them happy because I don't want players in my team who are not playing and they are happy.
"When you are not playing, you have to be upset and you have to be always trying to play.
"But it's my job. When I sign players, I sign good players and good people, I try to explain to them why they are not playing and why they are playing."