The Chilean has featured in all but one of Arsenal's matches this season, scoring 18 goals in 32 games, but is believed to be suffering from a slight hamstring strain.
Wenger does have the luxury of a fully-fit Theo Walcott and Mesut Ozil to choose from after the duo returned to the starting XI against Brighton, though, while new signing Gabriel is also available after completing his move from Villarreal.
Speaking about the Brazilian, Wenger told reporters: "I saw great quality. His level of concentration, he's quick, has great commitment and he's young.
"We are in a job where competition exists. The best player of the moment plays."
There was also positive news on the fitness of Jack Wilshere, with Wenger revealing the midfielder could be back in action in just under two weeks.
He added: "Jack is doing very well. He is a week ahead of schedule and should return in 10 days."
However Wenger is set to be without Danny Welbeck and Alex Oxlade-Chamberlain, with the latter expected to also miss the north London derby with Tottenham on February 7 after suffering a groin injury in the win at Manchester City.
