Stoke had a £750k bid rejected earlier in the season and are expected to renew their interest in the summer for the 25-year-old wide-man, who has played for Barbados.
The Brighton-born Ifill has scored 43 goals in 253 appearances for Millwall and is one of the few remaining members of the side which clinched promotion to the first division four years ago.
He came through Millwall's youth system, but ankle and Achilles injuries have stopped his progress this campaign.