The 29-year-old has started four matches for the Foxes this season, most recently in the 5-2 Capital One Cup victory over Carlisle United in August, and will join the Rams side in search of further first team action.
Whitbread will be available for the Rams’ Pride Park clash with Ipswich Town on Tuesday night, and could feature after defender Richard Keogh was sent off in the 1-0 defeat at Nottingham Forest on Saturday.
A product of Liverpool’s Academy, the Texas-born defender also spent four years with Millwall before signing for the Foxes after being released from Premier League side Norwich City in the summer of 2012.
Whitbread has made 21 appearances for Nigel Pearson’s side since signing, and scored one goal, which came against his new loan side in City’s 4-1 King Power Stadium victory over their East Midlands rivals in December 2012.