Gnabry is doubtful with an ankle knock suffered during last weekend's 2-0 win at Crystal Palace after coming off the bench to help the Gunners stay top of the Premier League.
Wenger declared that he will give the German starlet every chance to prove his fitness, as he looks to get the right blend of youth and experience to beat the Blues in tonight's fourth-round tie.
He told the club's official website: "Serge Gnabry has a problem, he got a kick on the ankle. He will be assessed tomorrow.
"After that we will decide who plays and who doesn't play. I will decide [on Tuesday]."
The 18-year-old capped a breakthrough start to the season by signing a new long-term deal yesterday.