Darren Ferguson moved swiftly to secure De Laet's services after Sean St Ledger and Callum Davidson both picked up knocks against Hull last Friday.
The length of the deal is yet to be agreed between the clubs but the versatile defender join fellow United youngsters Joshua King and Matthew James in North End's squad for Saturday's trip to QPR.
It is hoped the 21-year-old will be the first of three signings at Deepdale this week, as Ferguson looks to inject some depth and quality into a squad that is currently bottom of the Championship.
North End chairman Maurice Lindsay told the Lancashire Evening Post: "We've agreed a deal with United for Ritchie de Laet - it's been sanctioned by them. We've just got to finalise the length of the loan then everything will be done.
"He's joining us for training today and will be available for the QPR game.
"Ritchie is a versatile defender, he spent a month on loan with Sheffield United recently so he knows the Championship.
"We're still hopeful that we can reach an agreement with Stoke for one if not two of their lads, Michael Tonge and Danny Pugh.
"That would give us new faces and freshen up the squad for Saturday."
De Laet was signed in January 2009 by Manchester United from Stoke and has made three Premier League starts for Sir Alex Ferguson's team.
Source: Team Talk
Source: Team Talk