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.
Initially ruled out for 12 weeks, Foster is now approaching the end of his 15th week in recovery, although he is closing in on a return.
Although undoubtedly Albion's number one, once completely fit Foster has to first depose Boaz Myhill from the first-team before trying to force his way into England boss Roy Hodgson's plans for Brazil.
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."
Although Foster is seemingly behind schedule with regard to a comeback, Clarke insists that is far from the case as the initially diagnosed period of time out was a ballpark figure.
"There have been absolutely no complications," stressed Clarke.
"It's just been a little bit slower than we thought because medicine and recovery from injuries is not an exact science.
"On the 12-week mark he was getting close and since then his progress has been good. He's not too far away.
"But I won't tell you he'll be ready in a week, two weeks, three weeks or four weeks. I'll just wait and let nature take its course."
Foster is joined on the sidelines for Wednesday's visit of Manchester City by Youssouf Mulumbu, with the midfielder suspended for one match after collecting five yellow cards.
Winger Scott Sinclair, on-loan from City, is unavailable against his parent club, albeit is sidelined anyway with a hamstring problem.
After suffering a 2-1 defeat at Newcastle on Saturday, Clarke sees no reason why Albion cannot bounce back with a win over a City side that has only collected four points from a possible 18 away from home this season.
"If you are playing against a top team with world-class players like Manchester City you probably need them to be a little below their best and we have to be very close to our best," said Clarke.
"But we've shown on a number of occasions that happens quite a lot to us."