Gayle was a target for Slavisa Jokanovic’s side in the summer but they failed with a £15m move. The Magpies are keen to raise cash from the sale of the Serbian, who spent the final three months of last season on loan at Fulham, helping the Londoners beat Aston Villa 1-0 and win promotion via the play-offs.
Mitrovic is just two days from a return to training on Tyneside - where he has no future under boss Rafa Benitez - because the long-standing transfer has yet to be completed.
The 23-year-old scored 12 goals in 17 Championship appearances for Fulham last season, and the west London club are keen to sign him on a permanent basis.
According to the Mirror, the two parties have agreed personal terms but the deal is still far from being finalised, although further progress is expected over the next seven days.
However, reports suggest that Gayle is a reserve option for Fulham if the transfer of Mitrovic collapses.
The Cottagers are still hoping to get a deal over the line for Mitrovic although various sources have suggested they would consider a move for the former Crystal Palace star Gayle as a potential alternative.
The Serbia international wants to join Fulham and get regular game time as he has been on holiday since playing at the World Cup in Russia.
London-born Gayle has struggled for consistency at Newcastle and could be tempted by a return to the capital if Fulham come calling before the end of the transfer window.
Benitez is hoping for a breakthrough this week after admitting he needs another five signings before the window closes at 5pm on August 9 - the day before the top flight season begins.