You can appreciate Nigel Clough's reluctance to discuss whether Sir Alex Ferguson is Britain's greatest football manager. For the third time in 40 days this afternoon, the Derby manager will go head-to-head with Ferguson when his side meet Manchester United in the fifth round of the FA Cup at Pride Park.

So far the honours have been split, with each winning the home leg of their Carling Cup semi-final last month – United prevailing 4-3 on aggregate – to reignite a rivalry between the families that stretches to when Nigel's father, Brian, faced Ferguson in the dugout.

The then Nottingham Forest manager was beaten overall in that contest, claiming six wins from 16 encounters to Ferguson's seven. Since the most significant of those victories for United's manager, a 1-0 FA Cup triumph at the City Ground in January 1990 that many claim spared him the sack, the Scot has gone on to win everything in the game.

"It's difficult for me to say with my family connections," Clough says. "He is certainly up there. It's easier in some ways being at United, the biggest club in the world. He's never been afraid to spend money, and when you're at the biggest club in the world, why not?"

Not that Derby feel intimidated by their opponents today – Clough believes they can repeat the heroics that saw them beat United only a month ago despite losing Jay McEveley to suspension and Luke Varney to a groin strain.

"In a one-off cup tie, lightning can strike twice," Clough says. "That may be counterbalanced by United's determination to put things right from the last time. I'm sure they won't want that to happen again, so we're going to have to produce something close to that, if not better, in order to get a result."