Both clubs have a verbal agreement in place, but it does not include a purchase option or obligation, and Tierney is expected to return to Arsenal at the end of the season.
Sociedad are expected to pay a loan fee, although the finances involved are closely guarded for now. They will also cover the defender’s salary in full for the duration of the loan.
Tierney’s imminent departure stems from a desire for regular first-team football, which Gunners boss Mikel Arteta cannot guarantee at the Emirates Stadium.
The Scottish full-back already had the experienced Oleksandr Zinchenko to contend with for a place in the starting line-up, and Jurrien Timber’s arrival only made things more complicated.
Although naturally a centre-back, the highly-rated Dutch youngster is comfortable with both feet, making him capable of featuring on either side of the defence.
Tierney is yet to feature in the Premier League for Arsenal this season, having failed to make the cut in either of Arteta’s matchday squads thus far.
His last start for the Gunners came in the 3-0 league defeat to Brighton & Hove Albion last season, but he made an appearance in this season’s Community Shield victory over Manchester City.
He was summoned from the bench late in the second half to replace Timber, who is now expected to spend six months in the treatment room following an anterior cruciate ligament injury.
Tierney has endured his fair share of injury problems, but he stayed fit for most of last season, making 36 appearances across all competitions.
He was also linked with a move to Newcastle United, but his temporary switch should allow him ample playing time and the chance to feature in the Champions League.
The 26-year-old is expected to travel to Spain for his medical examination over the weekend, and he will hope his time in La Liga helps revive his Arsenal career.
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