Derbyshire gave du Plooy his first opportunity in county cricket in 2019 and he has become one of their senior players during his five seasons at the club. He was appointed captain earlier this year but his contract expires at the end of the season, meaning other counties have been allowed to approach him for the last three weeks.
ESPNcricinfo understands that several counties have been in contact with du Plooy but Middlesex have emerged as frontrunners. He would be a vital player for them in both the County Championship and the T20 Blast, and is understood to be keen to test himself in Division One.
Mickey Arthur, Derbyshire's head of cricket, has been trying to convince du Plooy to sign an extension with the club and he is expected to make a decision in the next few days. If he chose to leave, he would be the second consecutive Derbyshire captain to leave the county after a single season in charge, following Shan Masood.
Du Plooy is not a household name but has an excellent record as a middle-order batter across formats and his stock is on the rise in franchise cricket. He played for Joburg Super Kings in the inaugural SA20 earlier this year and impressed coach Stephen Fleming so much that Fleming signed him for Southern Brave at the top salary of £125,000 in March's Hundred draft.
He qualifies as a local player in county cricket thanks to a Hungarian passport and pre-settled status in the UK, and at 28, he retains ambitions to play international cricket. He is expected to qualify for England next year, telling the Cricketer magazine earlier this year: "I'd love to play for South Africa if I could, and I'd love to play for England if I could."
Worcestershire recently confirmed the appointment of Ashley Giles as their chief executive, and convincing some of the county's best young players to extend their contracts appears to be his most pressing task.