Newcastle boss Rafael Benitez has been keen to make improvements to his first-team squad after promotion back to the Premier League, although he found himself frustrated with a lack of high-profile additions.
However, he has been successful in bringing in Spanish Under-21 international Merino ahead of the new campaign, and the former Osasuna player says that St James’ Park is the ideal place for him to continue his development.
The 21-year-old told the club’s official website: “It feels good and I’m very happy to be here, to be part of this club. I’m looking forward to touching the ball, meeting my new team-mates and starting to play football.
“I know it’s a great club and a really nice city. I had different options but I think this is the right place for me to play.”
In his first season at Dortmund, Merino made just two starts and six substitute appearances in the Bundesliga.