Berahino is believed to be at the centre of a bidding war between some of the Premier League's biggest clubs after enjoying a break-out season with 15 goals in all competitions.
Liverpool and Tottenham are thought to be interested in the 21-year-old England prospect, who angered fans last week when admitting that he would like to move on "to bigger things" should West Brom's top-flight status be preserved.
And with clubs circling, Foster conceded West Brom's hands may be tied when it comes to keeping hold of the talented youngster.
"Without a doubt I want him to stay but I completely understand if a team is going to come in with a £25-30 million bid," said Foster.
"There's not a lot you are going to do about that. As long as he keeps working his socks off and doing the business for us, I don't think anyone would begrudge him a big move like that.
"It is only going to benefit the club, a lot more money for us to invest into other players as well."
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