The Gunners are said to be making strong progress over a £25.3m deal for the Spain international, who proudly dons a Euro 2024 winners' medal around his neck and has made a name for himself in La Liga.
Mikel Arteta is thought to have been on the charm offensive to convince Merino that the Emirates is the place for him to thrive, and having now got the green light from the player, a verbal agreement with Sociedad is not believed to be too far away.
Merino will become the third signing of the summer for Arsenal after David Raya and Riccardo Calafiori, and here, Sports Mole looks at which shirt numbers the 28-year-old could take in North London.
Ever since he first sported the Real Sociedad jersey in 2018, following one season in the Newcastle strip, Merino has proudly worn the number eight shirt, coincidentally the same position he tends to occupy for club and country.
The 28-year-old will likely start on the left of Arsenal's midfield trident, as Declan Rice drops into a deeper position, but creator-in-chief Martin Odegaard has been in possession of the '8' since his permanent move from Real Madrid in 2021.
As club captain, the Norway international is in no danger whatsoever of losing his grip on the number eight shirt, unless he charitably donates that jersey to Merino upon his arrival, a scenario that is virtually impossible to envisage.
The '8' has been the shirt most commonly worn by Merino during his career, but the midfielder has recently sported the number six for European champions Spain, a jersey that defensive cornerstone Gabriel Magalhaes dons in North London.
The Brazilian should not be giving up that traditional defender's jersey either, but some notable numbers might free up in the next few weeks if some of Arteta's troops seal expected transfers elsewhere.
Fellow midfielder Thomas Partey has peculiarly sported the traditional number five shirt for defenders, but he might be on his way out, offering Merino the chance to follow in the footsteps of him, Martin Keown, Tony Adams and Steve Bould.
Alternatively, Merino might appropriately nab the jersey of the man he is arguably being brought in to replace, as Emile Smith Rowe is on the verge of a move to Fulham and will therefore abandon the number 10 shirt.
Of course, that scenario throws up the possibility of Odegaard moving from eight to 10, thereby vacating the former shirt for Merino, who could alternatively don the '10' also worn by Mesut Ozil, Dennis Bergkamp, Robin van Persie and - memorably - William Gallas.
While at Newcastle, Merino was the Magpies' number 23 - a shirt now freed up by Albert Sambi Lokonga's loan to Sevilla - while the 24 he wore at Borussia Dortmund will become available if Reiss Nelson leaves as expected.
In terms of currently available numbers, the '13', '16' and '17' are awaiting their next takers, although the former is usually reserved for goalkeepers in North London; the last Arsenal outfielder to wear it was Aleksandr Hleb.