Alexis Sanchez

Earlier this week, Sanchez admitted to struggling with mental exhaustionafter a disappointing start to life at Old Trafford, and even considered pulling out of Chile's friendlies with Sweden and Denmark.

"The change of club was something that was very abrupt - it was the first time I've changed clubs in January - but many things have happened in my life that are difficult," Sanchez told Chilean media on Thursday.

Both players are entering the final year of their contracts at the Emirates Stadium and have so far refused to sign extensions.

Sanchez is a target for Manchester City and was also linked to Chelsea late last season.

In what was billed as a must-win game for both teams for very different reasons, Arsene Wenger started with three at the back for the first time since 1997.

But it was through a sublime Sanchez free-kick that Arsenal took the lead before Alvaro Negredo equalised just after the break.

Ozil won the game for the Gunners with 19 minutes remaining as they moved to within seven points of Manchester City in fourth with a game in hand.

The Arsenal man signed for the Gunners from Barcelona in the summer of 2014 for £35million, and has since been a roaring success at the Emirates.

And Pellegrini, who left Manchester City in the summer to be replaced by Pep Guardiola, said the club were punished by UEFA for breaching FFP rules, and did not have space in the squad for him.

"He was one of the best in the world and he showed it every day," Pellegrini told Chilean radio station ADN. "He was a major player we wanted to take to City.

Having set up Mesut Ozil for Arsenal's opener on 24 minutes, Sanchez capped a stunning individual display with three goals in 15 second-half minutes.

Andy Carroll's marked his long awaited return to the West Ham first-team with a goal nine minutes from time but Alex Oxlade-Chamberlain's response a minute later ensured it was mere consolation for the hosts, who remain a point above the relegation zone and without a league win since mid-October.