The striker scored his 15th goal of the season on Wednesday when the Baggies beat Swansea 2-0 at the Hawthorns.
Keeper Foster said: “Without doubt I want him to stay but I completely understand if a team is going to come in with a ??25-30million bid.
???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.”
And Foster hopes that the 21-year-old Berahino will remain grounded despite all the publicity he has received.
Foster added: “There is always a case when a young player scores a few goals, there is always so much hype about it.
“I don’t care who you are, if you are Harry Kane at the moment, the pressure on him is incredible. I know he is scoring goals. It’s just too much sometimes.
“Everyone needs to take a step back and let them do their thing and hopefully Saido can relax into that mould a bit more and just do his thing.”