Millwall have submitted a new offer, worth in the region of £2m including add-ons, for Hibernian's Kevin Nisbet.
The Championship club had previously offered just over £1m for the 25-year-old Scotland international.
The latest offer will now be discussed by Hibs owner Ron Gordon and chief executive Ben Kensell.
But Ryan Porteous' potential move to Watford may be on hold until the full extent of the injury to fellow centre-half Rocky Bushiri is established.
The terms of the move to Millwall would be life changing for Nisbet, who has scored seven goals in the seven appearances since making his return from surgery on a knee injury.
Nisbet joined the Scottish Premiership club from Dunfermline Athletic for a fee of £250,000 in July 2020 having scored 23 goals in 32 appearances for the Fife club.
The Glaswegian has since earned 10 Scotland caps and played 88 times for Hibs, scoring 34 times, leading to interest from the club sitting eighth in England's second tier.
Millwall are looking to strengthen their front line after selling Isaac Olaofe to Stockport County and terminating the contract of fellow striker Benik Afobe this month.
Scotland cap Porteous has already told Hibs he has no intention of signing a new contract when his current deal expires in the summer.
However, Hibs are waiting for the results of tests on Bushiri after the Belgian-born defender was carried off during Sunday's Scottish Cup defeat after a challenge by Heart of Midlothian midfielder Cammy Devlin.
Porteous, who turns 24 in March, would be able to move on this summer with no compensation required to be paid.
Therefore this is the last transfer window the Easter Road club would be able to cash in on the player who has come through their youth system since signing professionally aged 16.
Kevin Nisbet has spent a year and a half at Easter Road