Speculation continues to link the Holland international with a move to Chelsea and Liverpool, with the defender last week taking matters into his own hands by handing in a transfer request.
Van Dijk has been training away from the main group as he attempts to force an exit, but Saints chairman Ralph Krueger insists the defender is "not for sale in this window".
"Virgil is not for sale in this window and it's not personal," the chairman said, just days after the Gao family bought an 80 per cent stake in the club.
"It's not about him, it's about an overall much, much, much bigger picture - a change of course for Southampton.
"We want to mature, we want to be a team that can profit from synergies that create a much more attractive football and a better product for the fans, and gives us a chance to get back into Europe.
"We are very, very adamant about carrying this through. The new partnership has completely and wholly backed our strategy and plan and on September 1 people will see how serious we were and are."
Antonio Conte is keen to bring in a new central defender before the closure of the transfer window, but will have to look elsewhere as Saints are clearly in no mood to do business.