'If they are promoted then major surgery is needed on the squad,' said Roeder.
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'That is not putting a dampener on anything this season it's me telling the truth how I see it and not brushing it under the carpet.
'When you are in the game, most managers and coaches do that. But when you are out of the game it's easier to speak your mind and say it how you see it. That's the reality of it.
'Sometimes you are better to have somebody who is detached from the actual inner sanctum to make these assessments.
'There are two or three players that need replacing because they are past their sell-by date. The sands of time stand still for no man.
'Even King Canute couldn't stop the tide coming in we're all getting old and we have to accept it's a young man's game.'
Roeder, who also captained Newcastle during the 1980s, continued: 'I'm saying the gap between the Premier League and Championship is as wide as it ever has been it's huge.
'That doesn't mean you won't get surprise results in cup matches between teams from the different divisions, but the majority of teams in the Championship wouldn't survive 38 Premier League games.
'It's been proven teams struggle when they go up unless they spend a lot of money on players. Generally you'll be in the bottom part of the table over 38 games.
'If the squad they have now pulled in the right direction, they would stay up next season but they would be involved at the bottom end of the Premier League again.'
Roeder also blamed players rather than Ashley for Newcastle's relegation last May.
'Last season, Newcastle was a shambles,' said Roeder, who has been out of work since being sacked as Norwich manager last January.
'Players may have used off-the-field activities as an excuse at times. But give a footballer one excuse to play badly and he will find another nine to go with it.
'They should not have gone down with the players they had.'
Roeder added: 'The only people I feel sorry for are the fans they don't deserve it.
'They are the best supported team in the world for loyalty.
'The true Geordie supporter's dad supported Newcastle and his granddad and his great grandfather.
'Newcastle haven't won a domestic trophy since 1955. I was born then I'm 54 in two weeks' time.
'They say football is a religion in Brazil, Italy and Argentina? It's more of a religion in Newcastle than anywhere, and it makes me feel like rubbish when I see them in the Championship.
'Thankfully, because there is such a different in the class gap, United look like they will bounce back at the first time of asking and then they have to see what investment is available in the summer.'