The Spanish forward joined the Gunners from Deportivo this time last year but managed just seven goals in all competitions in 2016/17, including only one in the Premier League, as Arsenal finished sixth to miss out on Champions League football.
The 28-year-old, who did manage a hat-trick for Arsenal against Basel in the European Cup, will now return to Spain’s La Liga with Deportivo for the remainder of the 2017/18 campaign.
Arsenal also saw Alex Oxlade-Chamberlain depart the Emirates Stadium on deadline day after a £35m move to Liverpool.