Roberto Martinez expects to be without Bryan Oviedo for a period of "two to three weeks".
The Everton boss also confirmed Leighton Baines, Muhamed Besic and Tom Cleverley are all closing in on their own respective comebacks, with Tony Hibbert and Steven Pienaar also eyeing full fitness in November.
With regards to Baines, Martinez disclosed he plans to field the left-back in a behind-closed-doors friendly during the international break in a bid to boost the England man's sharpness following ankle surgery.
Costa Rican Oviedo was withdrawn against Sunderland with a hamstring complaint last Sunday and had a scan on Tuesday afternoon.
And, updating on the situation at his press conference on Thursday morning, Martinez revealed the 25-year-old could return later this month.
"Leighton Baines, Mo Besic and Tom Cleverley have been training with normality with the first-team squad," said the Toffees chief. "That’s a real positive boost. It’s making sure we measure that well and don’t rush them back into action.
"With those three we’ll get a bit more information over the next few days. I don’t think Leighton will be available for the weekend - it’s a case of managing his match fitness more than anything else. Medically, he’s in a great condition.
"Bryan Oviedo picked up a hamstring problem that may keep him out of action for two to three weeks, but it’s nothing too serious. We hope that he can come back for the Aston Villa game. If not, the Bournemouth game.
"Steven Pienaar is working well as well but is not available for the weekend. Hibbo has had an injection just to take some pain away, but in the last three weeks he has been working with the first team, so I would expect him to be available after the international break."