He follows teenage centre-back and England Under-21 international Cresswell to The Den where he will work under Gary Rowett.
South London Press report Shackleton is due for a medical with his loan move set to be all tied up this week.
Unlike Cresswell’s straight loan deal, Shackleton’s switch could be made permanent next summer in a similar situation to Tyler Roberts who joined fellow London side Queens Park Rangers on loan earlier this window.
Shackleton’s Leeds deal expires in 2024 and has racked up 78 appearances across all competitions for his boyhood club since joining United at the age of seven.
Check out the latest Premier League transfer speculation below...
7. Gunners in for Zinchenko
Arsenal hold a ‘growing confidence’ that they will wrap up a £30m deal for Manchester City midfielder Oleksandr Zinchenko in the coming days. (Sky Sports) | Getty Images
8. Toon linked with Zapata
Atalanta are waiting for Newcastle United to make a move for Duvan Zapata, and could sell the striker for as little as £20m. (L’Eco di Bergamo) | Getty Images
9. Leeds close in on Perkins
Leeds United are set to sign promising talent Sonny Perkins amid ongoing discussions with West Ham about a fee for the midfielder. (The Athletic) | Getty Images