Arsenal goalkeeper Lukasz Fabianski is being monitored "day by day" after injuring a rib during Arsenal's 3-1 Premier League win against Norwich.
The Polish goalkeeper returned from a spell on the sidelines in the 2-0 Champions League win against Bayern Munich and retained his place as the club's first choice for the next four games, all of which Arsenal won, before missing the goalless draw with Everton earlier this week.
Now, though, it is unclear when Fabianski will return with the pain coming and going.
"Fabianski has a crack in his rib that has not moved, so we have to treat it clinically," Wenger said. "That means has he pain or does he not? That is day by day."
Wojciech Szczesny returned for Arsenal against Everton and Wenger was happy with his performance in keeping a clean sheet against the fellow top four hopefuls.
Wenger said: "He had a good performance, I was pleased with his focus, with his sharpness. He dealt well with the situation that he faced.
"In our job there is only one way to respond, to practice harder and stronger and show that you are ready for a fight, that is what he did."