Foster helped Blues win the Carling Cup six months ago via a shock win over Arsenal at Wembley but has witnessed the dramatic slump in fortunes since with sadness.
City were relegated from the Premier League, saw manager Alex McLeish and more than a dozen players leave and leading share-holder Carson Yeung charged with alleged money-laundering in Hong Kong.
It has left the supporters worried about what lies ahead and Foster believes they need to be put in the picture.
He said: "It is a big shame. I made no secret of how much I enjoyed it last season.
"Everything was so good at Birmingham. The fans were fantastic and there were some very big highs and very big lows at the end of the season.
"I've got a lot of friends within the club, not just the players but the staff as well, masseurs, physios, people like that.
"It is not only the players that have to be sold when relegation happens. It is people like that which lose their jobs as well which makes it quite sad as well."
Foster added: "Am I worried about the future of Birmingham? It is something that a lot of the fans are worried about. They need answers.
"They've been there for the club through thick and thin and the thing that is worrying is that there are not too many answers coming out.
"They (the club) just need to answer things to put the fans minds at ease."
Foster noticed how the effect of relegation had quickly swept through the club when he reported back for pre-season training.
He said: "In pre-season there was something like 12-15 players from last season who had already left.
"It was a massive change and one thing that comes along with relegation. It was very sad.
"Obviously the debts haven't helped. You see other teams like West Ham and Blackpool go down but they are in a lot more different situation.
"They have held on to some of their star players. Unfortunately it wasn't possible at Blues.
"I am a little bit worried for the club. I don't know all the facts to be perfectly honest. I don't think anyone really does.
"We are going to have to wait and see and hopefully it will all clear up."
Foster admits the move to West Brom was ideal in not disrupting his family life.
He said: "It was ideal in the fact I've not got to uproot. I've got a young family now.
"It is something I find very important, that I've not got to move half-way across the country and ship them about.
"I can live from home and commute like I do every day. Once I got here, I realised what a nice and well run club it is."
Foster temporarily retired from international football at the end of last season and is maintaining the same stance with England for the time being.
He said: "I haven't had a rethink at all. I found last season when I was just concentrating on playing football for Birmingham, that I seemed to get my best form out of me.
"I haven't re-thought it at all and am concentrating on playing club-level football."
Midfielder Zoltan Gera has rejoined Albion on a two-year deal - with an extra year's option - and admits being reunited with Roy Hodgson was a big factor.
Hodgson signed the Hungary international from the Hawthorns when in charge at Fulham three years ago.
Gera said: "I was quite happy here when I was here for four years. But Roy was a big part for me to coming back to this club.
"For me it was the perfect combination, West Brom and Roy. I can't ask any better."
Gera will miss the opening three games of the season through suspension after being sent off for the Cottagers in the final game of last season.
But he expects to be available for the clash with Norwich on September 11 as he steps up his fitness programme following ankle surgery.