Arsenal attacking midfielder Alexis Sanchez is fit and ready to face Chelsea but manager Arsene Wenger is ready to wait.
The 27-year-old last featured for the Gunners against Norwich City at the end of November.
He is expected to start on the bench tomorrow against Chelsea with Mesut Ozil certain to be in the starting line-up.
"I am cautious with him because we cannot afford a setback with him," Wenger explained.
"A setback would mean a very long period out so we don't want to take this gamble. The signs he has shown in training this week are positive.
"The doubt is that he has been out for a long time and the risk of a setback if you try to go too early.
"To be clear on all the tests is one thing, after he is clear on training is another things, and after the intensity of a big game you can never repeat in a training session.
"You can make sure after a certain amount of time that the risk is minimal."