The 33-year-old midfielder will retain his registration next season and could be used in the first team in emergencies, but he admits his playing career has all but drawn to a close.
Clark has made 265 appearances for United - 25 of them last season - and a further 263 for Sunderland and Fulham behind him spanning 16 years since he first broke into the senior ranks as a teenager in September 1990.
But having agreed to join Roeder's coaching team along with new assistant boss Kevin Bond, he is now preparing for a new phase of his career.
Clark: "I must admit I had to have a couple of days to think about the offer - not for the job I'll be doing, but because of the fact that I have to be realistic and admit that it just about signals the end of my playing days.
"I'll still be registered to play, but it will only be in emergencies. I know we said that last season when I came back to the club, but this time I think the whole squad will have to be injured for me to get a game. And if I'm not involved, then that means the team are doing well and we haven't got huge injury problems, so that's fine by me.
"I think with a job like this you have to be 100% fully focused on the coaching side of things, and that's what I intend to do. I've had my hernia operation, which went really well, and will take part in the pre-season training with the rest of the lads, and there is a chance of a few reserve games depending on how things go.
"But coaching will be the priority for me now. After 17 years as a first team player, it is a bit of a wrench and it is sad in a way. I knew there were other clubs interested in taking me and giving me the chance to prolong my playing career, but at the end of the day it was too good a chance for me to turn down.
"I've always said this is my club, and I'm looking at it as one chapter closing and another one opening for me."