Nacho Monreal has left Arsenal to sign a two-year deal with La Liga side Real Sociedad while Mohamed Elneny has joined Besiktas on a season-long loan.
Monreal, 33, started Arsenal's first three games of the season and captained the team against Burnley.
The Spain international played 250 Arsenal games, scoring 10 goals, after joining from Malaga in January 2013.
Egyptian midfielder Elneny, 27, made 89 appearances after arriving from Basel in January 2016.
Manager Unai Emery said on Thursday that Monreal could leave the Gunners before the European transfer windows shut.
The left-back won three FA Cups during his time with Arsenal and helped them reach last season's Europa League final.
He made his international debut in 2009, has won 22 caps and was a member of Spain's 2018 World Cup squad.
Arsenal signed Kieran Tierney, 22, as his long-term replacement this month.
The former Celtic left-back is yet to make his Gunners debut and is not fit enough to be considered for Sunday's north London derby against Tottenham.
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