The goalkeeper's good form, plus an injury to Nottingham Forest's Darren Ward, gives Margetson his chance.
Whoever wins this semi-final will meet the victors of the tie between Nottingham Forest and Yeovil.
And McDonald's squad showed their potential by coming through two matches against promotion-chasing Nottingham Forest unbeaten.
BBC: SPORT | Football | My Club | Carlisle United | McDonald keen to play down hopes
Nottingham Forest were also keen to sign the long-time Rams target and spoke to the 26-year-old.
The Magpies are guaranteed at least a top-two finish after Nottingham Forest drew 0-0 with Cardiff.
With Nottingham Forest, Clough and Taylor won the European Cup twice, in 1979 and 1980.
The final will take place at Nottingham Forest's City Ground for the fourth year in succession.
Scunthorpe travel to Nottingham Forest on Saturday before hosting Portsmouth on the final day of the season.
The Addicks lost 2-0 to relegation rivals Nottingham Forest on Saturday and are eight points from safety.
Seventh-placed Blackpool's 3-1 win over Nottingham Forest means Swansea's lead over them remains a slim two points.
Barnsley frustrated new Nottingham Forest manager Steve McClaren to earn a deserved point in an uninspiring draw.
Championship sides Newcastle, Nottingham Forest and West Brom had also been in the hunt to sign him.
Marlon Harewood bagged a hat-trick as Nottingham Forest romped to victory over Gillingham at The City Ground.
"He will get back to how he was, knowing him as I do, " insisted Nottingham Forest full-back Gunter.
He said the approach to charity work by Nottingham Forest had changed dramatically in the past few years.
The former Nottingham Forest star, 42, has joined the Championship strugglers after 10 years at the non-league side.
Former West Brom boss Megson, 48, has been out of work since leaving Nottingham Forest in February 2006.
Clough and his assistant Taylor also enjoyed success at Nottingham Forest, winning the European Cup in 1979 and 1980.
Boyd is currently on loan at Nottingham Forest and has one year remaining on his contract at London Road.
His previous job ended when he resigned as Nottingham Forest boss in 2004.
Posh allowed George Boyd to make the move to Nottingham Forest on Tuesday.
Nottingham Forest defender Chris Gunter is also out as is Blakpool's David Vaughan.
Nottingham was included in England's bid despite Nottingham Forest's existing City Ground being too small and having inadequate access.
Stewart, capped three times for Scotland, had previously been farmed out by United to Royal Antwerp and Nottingham Forest.
The Japan international looked sharp as Tottenham's reserves beat Nottingham Forest reserves 2-1.
The former Nottingham Forest and Norwich City striker was found hanged in a London garage in 1998 at age 37.
Ninety-six Liverpool fans died after the crush at Sheffield Wednesday's stadium during the 1989 FA Cup semi-final with Nottingham Forest.
Northampton chairman David Cardoza revealed his delight at securing the services of the former Nottingham Forest and Aston Villa left-back.
BBC: SPORT | Football | My Club | Northampton Town | Northampton name Gray as manager
He was subsequently linked to positions at Sporting Lisbon, Nottingham Forest and Reading, but decided to delay his return to management.
It also highlighted the subsequent cover-up by South Yorkshire Police following the 1989 FA Cup semi-final between Liverpool and Nottingham Forest.
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