Last season, he played 36 games on loan at Dutch top-flight side ADO Den Haag.
"With the World Cup in June, it is important to have the chance of playing regularly," Omeruo told BBC Sport.
"Hopefully I can help Middlesbrough fight for promotion - nothing is impossible in football.
"Training with the first-team at Chelsea is just not good enough for my progress and development.
"More significantly, I was highly recommended [to Karanka] by Jose Mourinho and that feels good.
"They [Karanka and Mourinho] speak to each other on a daily basis so I believe I'll be in good hands.
"Apart from playing regularly and helping the team, this provides me with an opportunity to be sharp for the World Cup."