Reading pair Sean Morrison and Jordan Obita have both signed new contracts at the Madejski Stadium.
Ipswich defender Aaron Cresswell has signed a two-year extension to his contract.
Press Association Sport understands the 52-year-old's appointment will be announced on Monday afternoon.
McClaren will replace Nigel Clough, who was sacked on Saturday in the wake of a 1-0 derby defeat at Nottingham Forest.
His arrival at Pride Park will mark the completion of a circle for the man who guided Middlesbrough to Carling Cup glory and FC Twente to the Dutch title.
McClaren played for Derby and returned to make his name as a coach with the Rams under Jim Smith before getting his big chance at Manchester United.
McClaren, who was in charge of England for 18 months after succeeding Sven-Goran Eriksson in 2006, has been working as first-team coach at QPR since July.