N'Gotty and Nielsen have become Martin Allen's first signings

N'Gotty, 35, joins from Birmingham - who had offered him a new contract.

Ex-Denmark Under-21 stopper Nielsen, 29, who joins from Aalborg, had a brief spell with Millwall in the 1990s.

Also arriving is ex-Blackburn boss Don Mackay, who leaves his current job as Middlesbrough's chief European scout to take up the role of sporting director.

Mackay has also managed Dundee, Coventry and Fulham, was director of football at Airdrie and has also been part of Arsenal's scouting network

"I am looking forward to working with him and picking his brains to help me develop," Allen told the club website.

"Both new players have a wealth of experience and I believe they will be major assets for the season ahead."

On their way out of the Walkers Stadium are defender Alan Maybury, midfielder Stephen Hughes and striker Elvis Hammond, who have all been transfer-listed.

Maybury, 28, and Hughes, 24 were signed from Hearts and Rangers in January 2005, and striker Hammond, 26, signed from Fulham in August of that year.

"It is nothing personal, nothing they have done wrong, but I have got to make changes," Allen added. "People on the periphery may have to make way."