The club are second from bottom in the Premiership, three points away from safety, having won just five times this season.

"The decision made by the chairman and the board of directors was unanimous and Colin has been aware the chairman was not happy with the way things have been going," chief executive Keith Loring told the club's official website.

Todd was appointed Derby's assistant manager in October 2000 and a year later he replaced Smith.

For the 17 games that Todd was in charge, Derby lost 11 times.

Over the weekend there had been intense media speculation that the club were preparing to appoint striker Fabrizio Ravanelli.

But Loring denied talks had been held with the Italian.

"I want to make it absolutely clear no conversations have taken place with Fabrizio Ravanelli concerning a managerial or coaching position at Derby County," said Loring.

"Quite simply no discussions have taken place with anyone regarding Colin's replacement."

Ravanelli himself said he was shocked by the news of Todd's departure.

"I'm very sorry for Colin Todd because he's a nice person who's always been very nice to me.

"He's had bad luck at Derby but that doesn't mean he will not have good luck elsewhere."

Derby are due to hold a board meeting on Tuesday when they are expected to discuss Todd's successor.

In the interim, reserve team manager Billy McEwan is to take charge of the team as they prepare for Saturday's home game against Ipswich.