Sanchez, who failed to score in his first eight appearances of the season, has scored six goals in his last three matches for Arsenal including a hat-trick against Leicester City and two against Manchester United when the Gunners won 3-0 in their last match on Oct.4.
He injured his hip in that match but played in both of Chile's World Cup qualifiers in the last week scoring in the 2-0 win over Brazil and grabbing another two goals in the South American champions' 4-3 win over Peru.
Wenger, speaking at his pre-match briefing on Thursday said that he did not know if he would be fit to face Watford, whose training ground is next to their own in rural Hertfordshire, just outside London.
"He came off as you have seen against Manchester United with a hip problem, a problem with the rotator muscle, but he wanted to go (to Chile).
"He played in the last two games and we have to see how he comes back but it is always a tricky situation. Chile were playing official World Cup qualifiers and he is an important player for them so they will use him if they can.
"He is a guy that always wants to play so I knew that was always going to be a tricky situation."
Wenger also said that defender Laurent Koscielney was having a test to see if he would be available following the hamstring injury he picked up against Olympiakos Piraeus in the Champions League at the end of last month, but that Mikel Arteta and Mathieu Flamini had recovered from their knocks and were available for selection.
"We have three players who could come back and be available again and I don't think we lost anybody from our last game," said the Frenchman.
Wenger was attending Arsenal's annual general meeting later on Thursday.
(Reporting by Mike Collett, editing by Mitch Phillips)
