Sky Sports understand that Barnsley have accepted an offer from League One table-toppers Charlton for Danny Haynes.
The Tykes announced at the turn of the year that they deemed the striker to be surplus to requirements and available for transfer.
Interest in his services has built steadily since then, with Millwall the first to make their move.
Lions boss Kenny Jackett revealed on Thursday that he had made an approach but was yet to hear back from Barnsley.
It is understood that Millwall were looking to reach a loan agreement, and the Tykes are keen to sell.
Charlton have put money on the table, and they have received a response from Oakwell.
The Addicks are looking to increase their firepower for the second half of the season, with the club on course to secure a return to the second tier.
They believe Haynes would be a useful addition to their ranks and discussions regarding a switch can now begin, with Barnsley having opened the door.