The news on Aaron Ramsey’s latest hamstring strain is, however, less positive with the Gunners midfielder certain to be out for a fortnight at the very least.
Sanchez and Ramsey both had to be taken off in the second half of Arsenal’s 2-1 win against Leicester on Tuesday.
Sanchez suffered a bang to his knee during the first half at the Emirates Stadium and Arsene Wenger was ready to substitute him at half-time but the Chilean insisted he could continue.
The 26-year-old was returning from a two-week lay-off with a hamstring problem but his latest setback is more of an impact injury and considered to be only a minor knock.
Sanchez could even play in this weekend’s FA Cup fixture, although Wenger may choose to rest his leading scorer with a busy schedule to come.
Ramsey’s diagnosis is more severe.
The midfielder is undergoing tests from Arsenal’s medical team but will not return before the Champions League last-16 first leg tie against Monaco on February 25.
“It is his third hamstring injury this season,” Wenger said after the game against Leicester. Last year it was a thigh injury but this year it’s a recurrence of hamstrings. You cannot say it’s not a worry because after a while the player doesn’t play with the freedom in the mind.
“He’s not overplayed. Before I just played him in every game but since he’s had these problems, I’m a bit more cautious with him.”
Meanwhile Middlesbrough boss Aitor Karanka is hoping old friend Mesut Ozil has an off-day on Sunday as he attempts to pull of another major FA Cup shock.
Championship leaders Boro head for Arsenal having stunned the nation with their 2-0 fourth round victory at Manchester City and intent on serving up a repeat in north London.
However, if they are to do so on Sunday, they may have to get to grips with Ozil, who scored a stunning opener in last weekend’s 2-1 derby defeat at Tottenham. The pair worked together during their time at Real Madrid, where Karanka served as Jose Mourinho’s assistant.