The England international was injured in a challenge from Adam Le Fondre in the opening minutes of Everton's 3-1 victory over Reading at Goodison Park.
He had to be immediately replaced, and Moyes said: "I genuinely haven't seen it again but I thought on the pitch it didn't look good. Jagielka knew about it and it is a bad one. He will have surgery tonight to stitch up his ankle."
He added: "It is a bad one because he is a key player for us."
- Sports & Recreation
- Adam Le Fondre