Newcastle United have exercised an option to buy Spanish midfielder Mikel Merino, converting his loan move into a permanent transfer with immediate effect.

The 21-year-old, who initially joined the Magpies on loan from Borussia Dortmund in July, has now committed his future to United, penning a permanent five-year deal which will keep him at St. James’ Park until 2022.

Since arriving on Tyneside, the highly-rated Spanish under-21 international has impressed, featuring in all seven Premier League games so far this term on his way to winning the FUN88 Player of the Month award for August.

During his time at Newcastle, the former Osasuna man has also made three appearances for Spain Under-21s, scoring twice – including his strike in their 4-1 win over Slovakia on Tuesday.

“I’m really happy to be here, and for this part of the contract to finally be official. I’m happy to be here for five more years and I hope to keep playing for this club and to give good things to all the people and the club,” he told NUFC TV.

“I have been focussed on football always, but it’s good to know it’s now official and people will know it. I’m focussed on my displays and improving myself, and I’m really happy to have signed this contract.”

Manager Rafa Benítez added: “I’m really pleased we have been able to bring Mikel to the club permanently. He has played very well since he joined us. He has settled in quickly, has a lot of quality on the ball and is keen to learn – that is a crucial part of his future development.

“He has made a great impression at the club, and he is a good professional. He has confidence, but he is still young and has things to improve. He has to keep working hard and playing well, and hopefully he can improve and enjoy playing here.”