Here, the PA news agency looks at the Chilean's remarkable career in England of mostly highs at Arsenal and lows at United.
Arsenal – The Highs
There is no doubt Sanchez was outstanding for the Gunners in the three years following his £30million move from Barcelona in the summer of 2014. In all he scored 80 goals for the club in 166 appearances, 25 of which came in an impressive 2014-15 debut season and 30 in a prolific 2016-17 campaign. The quality of his finishing was also, often, a particular delight. Fans will instantly recall a hat-trick – completing dummy and chip against West Ham and a backheeled finish as one of two goals against United. There were other deft chips and Panenka penalties among many fine strikes.
Other telling contributions
As well as the goals, Sanchez delivered in other areas of the pitch. With 45 assists to his name, Sanchez was involved in more goals than any other Arsenal player during his time at the Emirates Stadium. For Barcelona he scored 47 goals in 141 matches with 36 assists, meaning Arsenal enjoyed the best years of his career.
Sanchez was electric with the ball at his feet. His ball control was magnificent and, combined with his speed of thought, often bamboozled opponents. His flicks and tricks seemed fancy but were backed up by substance of performance. Goals often came in gluts and in style. He scored more than one goal in a game on 15 occasions, including two hat-tricks.
Sanchez helped deliver silverware in the closing years of Arsene Wenger's reign. His performances often lifted the team and he scored in both the FA Cup final victories of 2015 and 2017, against Aston Villa and Chelsea respectively. By contrast he won nothing at United.
Arsenal – The Low
Reaction to failed move
The biggest complaint about Sanchez from his spell at Arsenal centres around his performances in the first half of the 2017-18 season after a summer move to Manchester City failed to transpire. Sanchez had been expected to link up with Pep Guardiola at the Etihad Stadium but a potential £60million transfer broke down on deadline day as the Gunners failed to land their first-choice replacement Thomas Lemar. From then on, Sanchez's form nosedived, with ineffective, wasteful displays and an apparent negative influence on the team.
Man Utd – The High
Joining the club
There was plenty of excitement as United pulled off what appeared to be a coup to land Sanchez in January 2018. City were again interested and were favourites to sign him until baulking over wage demands. That cleared the way for United to make good on their interest and complete a deal that sent Henrikh Mkhitaryan in the opposite direction. United unveiled their star capture to much fanfare and with a video of Sanchez playing the piano and standing in the middle of a deserted Old Trafford.
Man Utd – The Lows
United signed Sanchez on a four-and-a-half year contract worth a reported £500,000 per week. In return Sanchez delivered just five goals in 45 appearances and contributed only nine assists.
Sanchez failed to spark in many of his games and his demeanour was poor. His poor returns led to rumours that his high wages were a source of disquiet within the squad. When United finished sixth in the Premier League in 2018-19, failing to qualify for the Champions League, he was targeted by many critics.
No specialist position
Whilst Sanchez delivered from numerous positions across the front line at Arsenal, particularly from the left or as a central striker, he failed to fit in at United. It was thought he would give them numerous options as a centre forward, number 10 or winger but, bereft of confidence, he failed to find a specialist role. Fans eventually got on his back and the problems worsened.