Reid, who played for Eire in last summer's World Cup finals, was given permission to talk to Blackburn Rovers earlier today and is set to hold talks with the Ewood Park outfit tomorrow.
"Obviously we don't want Reidy to leave," said Millwall chairman Theo Paphitis. "But the decision is now up to him and his advisors."
Reid will be seen as an obvious replacement for fellow Irish International Damien Duff and has been a long-time target for Rovers boss Graeme Souness. If the sale goes through, the 22-year-old midfielder will join up with former Millwall favourite Lucas Neill.