Doncaster have made forward Dany N'Guessan their sixth summer signing.
Tottenham have confirmed that Romanian defender Vlad Chiriches has completed a move to Napoli.
Palace boss Ian Holloway is keen to add a striker this week but appears to have lost out to Reading on Sheffield United's Nick Blackman.
The Eagles have also seen an enquiry for Wolves man Sylvan Ebanks-Blake rebuffed so are now set to turn their attention to Russell.
The 22-year-old Scot has 14 goals for the Tannadice club this season and is a Scotland Under 21 international.
But United would sell their prized asset for the right price and Palace could be tempted to act as they look to bolster their bid for promotion to the Premier League.