Foster, who has six caps to his name, has been on the sidelines since the end of August with a stress fracture to his right foot.
Offering the latest assessment on Foster, Clarke said: "Ben's been working outside for a couple of weeks now.
"He hasn't joined the group for full training, but he is working with the goalkeeping group which is another step in the right direction for him. He's progressing slowly, but progressing well.
"He's been seeing the light at the end of the tunnel for a while now, and for a goalkeeper when he starts to put his gloves on it starts to make him feel much better."
As for Foster's England prospects, Clarke added: "He's plenty of time, but first he has to get himself back fully fit, back in our training sessions.
"Then he has to work hard to get back into our team, and from there we can discuss any future possibilities for Ben.
"Right now, it's not for me to say (whether he can make the England squad). I will never, ever try to pick somebody else's team.
"For me and for Ben, the most important thing is he comes through the next week to 10 days' training, he joins in with the group and then we take it from there and see how he progresses.
"We can't look too far ahead, and I don't think Ben can look too far ahead either."
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