The Chile international has missed Arsenal's past two matches with a hamstring injury, including Saturday's 2-1 defeat to north London rivals Tottenham.
However, Sanchez - who has scored 12 goals in 21 Premier League appearances since arriving in a big-money move from Barcelona in the close-season - is back in contention for when Leicester visit the Emirates Stadium.
"Sanchez will be back in the group," manager Arsene Wenger said. "He's our best goalscorer. One of our hardest working players in the team. We missed him on Saturday, we missed his physical strength and work-rate."
The Frenchman also confirmed that midfielder Jack Wilshere has returned to training following a near three-month layoff with an ankle injury, but stated Alex Oxlade-Chamberlain (groin) will remain absent.
"We have to monitor him [Wilshere] daily and see how he develops. I don't know when he'll return," he added. "[Oxlade-Chamberlain] is not back. He's got at least two more weeks."
Arsenal's defeat at White Hart Lane came on the back of five straight wins in all competitions and just one defeat in 11 previous matches.
Wenger now sees Tuesday's match as the perfect opportunity to respond to the derby disappointment.
"We had a very strong run before Saturday so we just want to continue that. We need to respond strongly," he said.
"We have to deal with our performances. The criticism is always there. We have to focus on our performances.
"I don't take criticism personally. What I take personally is losing games. We have a good opportunity to show that we have the strength and quality to deal with pressure."
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