By Editor Wayne Veysey | Former Evening Standard, Press Association and Goal chief correspondent with 17 years experience of breaking big stories, including exclusives like this

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Alexis Sanchez has given Arsenal a major boost ahead of the demanding Christmas period, Football Insider sources understands.

The scan of his injured right hamstring will show on Wednesday that it is not as bad as initially feared and he should be back playing within three weeks.

Sanchez is set to miss Premier League clashes against Sunderland and Aston Villa, as well as next Wednesday’s must-win Champions League match at Olympiakos.

But he is hopeful of being fit for the showdown against Manchester City on 21 December for his comeback match.

The Chilean limped off with what Arsene Wenger confirmed was a hamstring problem in the second half of the Gunners’ 1-1 draw at Norwich on Sunday, prompting fears of a lengthy lay-off of four to six weeks.

But an Arsenal source has told Football Insider that the assessment of the club’s medical team is that the injury appears not to be a really serious one.

Sanchez grabbed the back of his his right leg 60 minutes into the Carrow Road clash after chasing a goal-scoring opportunity. He began to limp and then called for medical attention. He was immediately substituted and replaced by Joel Campbell as he was escorted off the pitch by physio Colin Lewin.

Sanchez’s injury came after Wenger revealed at his pre-match media briefing on Friday that the Chilean was struggling with a hamstring problem going into the match.

Laurent Koscielny (hip) also limped out of the Norwich match after just 11 minutes while Wenger revealed afterwards that Santi Cazorla “played on one leg for the final part of the second half” due to a knee problem.

Koscielny is in contention to face Sunderland at Emirates although Cazorla is expected to join Sanchez on the sidelines.

Red alert: Alexis Sanchez's hamstring injury might not be as bad as initially feared

Asked by Sky Sports on Sunday night if the amount of football Sanchez has played contributed to his injury, Wenger replied, “You could say that. At the moment on the striker front we have not much choice because [Danny] Welbeck is out, [Theo] Walcott is out, [Alex] Oxlade-Chamberlain is just coming back.

“Just because you repeat the games doesn’t mean you get injured, maybe the travelling to South America as well. I would have rested him today but he felt perfectly alright before the game and he declared that he had no problem.”

Of Arsenal’s 19 Premier League and Champions League matches this season, Sanchez has started 18 and been a second-half substitute in the other one, on the back of an exhausting programme over the last 18 months.