Derby are in the hunt for their sixth manager in three years following Gary Rowett's departure to Stoke.
The Rams missed out on promotion via the Sky Bet Championship play-offs this season for the third time in five years.
Here, we look at the early contenders to replace Rowett in time for the 2018/19 campaign.
Brentford boss Smith, 47, has been installed as the bookies' early favourite following his work with the London club since late 2015. The former defender, who signed a contract extension with the Bees in February until the end of the 2019/20 season, has guided them to three successive top-10 finishes in the Championship on a nominal playing budget. Smith, who had previously rescued Walsall from relegation in League One, gears his sides to play entertaining, attractive football and would be a popular choice among Rams fans.
Former Derby defender Stimac, 50, remains an iconic figure to Rams fans who voted him into their greatest-ever team in 2009 on the back of his four-year spell at the club until 1999. After an encouraging start to his managerial career with Hajduk Split and NK Zagreb, he had an unsuccessful stint in charge of Croatia's national team, which ended in his resignation after just over a year in 2013. Stimac has hardly set the world alight since, with indifferent short spells in the Croatian lower league, Iran and Qatar, with Sepahan and Al-Shahania respectively. His appointment would represent a huge gamble by Derby owner Mel Morris.
Republic of Ireland coach O'Neill, 66, has emerged as one of the favourites despite a trophy-laden playing career at Derby's East Midlands rivals Nottingham Forest. O'Neill, who has been in his current post since late 2013, won silverware in previous jobs at Wycombe, Leicester and Celtic and is renowned for eking the best out of his players. But he resigned at Aston Villa after growing frustrated and was sacked by Sunderland earlier in 2013. It remains to be seen whether the Northern Irishman still has the appetite to lead a side in the dogfight that is the Championship.
Simpson, who spent five years as a Derby player until 1997, led England Under-20s to World Cup glory in South Korea in 2017 and is currently in charge of the country's Under-19s. The 51-year-old also worked as coach at Derby in Steve McClaren's first spell as boss and has vast experience of managing in the lower leagues with spells at Rochdale, Carlisle, Preston, Shrewsbury and Stockport. Simpson's star has risen since his success with the national team's coaching set-up and may feel he is ready to return to club management and make an impact at a higher level.
McCarthy, 59, has twice won promotion to the Premier League and is in the hunt for a new challenge after falling out with Ipswich's fans and departing the club in April this year. The former Republic of Ireland boss would not be fazed by the expectation at Derby and his no-nonsense, pragmatic approach to management could appeal to Morris if stability is key to his next appointment. McCarthy won the Championship with both Sunderland (2005) and Wolves (2009) and has a point to prove after his five-and-a-half-year spell at Ipswich ended in acrimonious circumstances.