Ashton suffered the injury on Monday, Gianfranco Zola’s first day as West Ham boss.
Ashton told the Sun: “Unfortunately I’ve picked up another injury.
“I sprained my ankle in training on Monday and I’m looking at spending the next three to four weeks on the sidelines.
“I just went over on it. It happens to a lot of players.
“It’s not too serious but it will take a few weeks to heal properly.
“I’m looking at about three weeks and then it’s the international break. Hopefully I’ll be back after that.”
