Neil Warnock had been desperate to find the right man for the job after Kevin Blackwell ditched Bramall Lane for Elland Road (Leeds United).
Neil Warnock
"It was a big blow to lose Kevin and [physio] Dean Riddle to Leeds, but I've had to get on with it and it was important to get the right man," Warnock told www.sufc.co.uk.
"There were three or four good applicants for the job but David has been at the club before, he is a likeable man and has charisma, which I think is important.
"I spoke to (Tranmere Rovers manager) Ray Mathias about approaching David, but he wasn't forthcoming.
"David resigned because he wanted to talk to us, we then spoke over the weekend and hopefully the situation will be resolved at the end of the week."