Arsenal have completed the signing of Spain midfielder Mikel Merino from Real Sociedad.

An agreement in principle was struck on Thursday night between the clubs for an initial £28.4million transfer with a further £4.2m in add-ons, the PA news agency understands.

Merino completed his medical over the weekend and has been unveiled as an Arsenal player on a long-term contract.

Boss Mikel Arteta told the club’s official website: “Mikel is a player who will bring us huge quality with his experience and versatility.

“He has played at the top of the game at both club and international level for a number of seasons now.

“Mikel will make our squad significantly stronger, with his technical ability, together with his strong and positive character and personality.

“As we all saw in the summer, Mikel is also a winner, with his strong performances throughout the Euros helping Spain win the tournament.

“We are delighted to welcome Mikel and his family to the club and can’t wait to start working with him.”

The 28-year-old started his career at Osasuna before brief spells with Borussia Dortmund and Newcastle followed.

After a solitary season with Newcastle under Rafael Benitez, Merino returned to Spain to join Sociedad where he established himself as one of the best midfielders in the country.

International recognition followed and after Merino helped Spain win an Olympic gold at Tokyo in 2021, he played a key role in the nation’s Euro 2024 triumph last month and scored a 119th-minute winner against Germany in the last eight.

Merino departs Sociedad after 242 appearances, scoring 27 goals, and becomes Arsenal’s second major summer signing after Italy defender Riccardo Calafiori joined from Bologna.

Arsenal sporting director Edu said: “We are so happy to have completed the transfer of Mikel Merino. This has been another great team effort from many people at the club to finalise the transfer of a player who attracted interest from a number of clubs over the summer.

“Mikel was a key target for us this summer, and we identified him as a player who can fit perfectly into our squad and profile to improve us, as we aim to build on our strong performances of last season.

“With Mikel’s arrival, he brings us an added high quality of experience, physicality and athleticism as we look forward to this season ahead.

“We welcome Mikel and his family to the club, and look forward to seeing him play in the Arsenal shirt.”