Lee Gregory has handed in a transfer request at Millwall in order to push through a move to Rotherham, according to Sky sources.
The Sheffield-born forward is keen to move back north and the clubs are now expected to complete a deal.
Gregory, who is currently contracted at The Den until next summer, scored 27 goals in all competitions last season as Millwall reached the Sky League One play-off final, losing 3-1 to Barnsley.
The 27-year-old joined Millwall in August 2014 from non-league Halifax, where he played alongside England forward Jamie Vardy, and has scored a total of 36 goals in 95 appearances.
Rotherham manager Alan Stubbs, who was appointed as Neil Warnock successor in May, is currently shaping his squad ahead of the new Sky Bet Championship season and has already secured the services of Irish winger Anthony Forde.
Stubbs has turned his attentions to Gregory after failing with a bid to sign former Hibernian striker Anthony Stokes, who joined league rivals Blackburn.