Keegan opened the debate in the wake of Newcastle's defeat by title contenders Chelsea on Monday and Keane has now voiced the opinion that even clubs with £50million to spend this summer could only scratch the surface.

Keegan caused something of a stir with his outburst which has been polarising since, and he may have to explain himself to Magpies owner Mike Ashley at a meeting in London on Friday.

But Keane knows exactly where he was coming from.

Asked if he agreed with Keegan's assessment, he said: "Of course, 100%, £50million wouldn't get you into the top four, nowhere near it.

"Kevin Keegan is a clever man, he knows the score, and I think everyone agrees with him on that.

"Anyone who disagrees with it doesn't know football. Fifty million won't get you anywhere near the top four."

Keane has invested £44million this season in an ultimately successful attempt to keep his promoted side in the Premier League.

Having done that with something of a struggle, he has made no secret of the fact he believes it will take as much again, if not more, to mount a more forceful challenge next time around.

However, he knows the task of establishing the club as a genuine power in the top flight could take several years.

He said: "I am certainly not looking to compete with the top four next season, but we want to be competing with the teams just ahead of us.

"We want to be up against the Man Citys and the Blackburns and even the Villas, trying to compete with them on a regular basis.

"We have done in a one-off game against them. We lost to Blackburn twice by the odd goal, City twice by the odd goal.

"You look at Middlesbrough, who have been in the league a lot longer than us - they are the teams we want to be certainly challenging more next season."

He added with a smile: "But the big four - not for another two years at least - no, not for a long time yet.

"But I know where Kevin Keegan is coming from. To me, it is obvious."

Keegan has also warned that the Premier League is in danger of becoming "boring" if the current big four continue to dominate, although Keane, a veteran of Manchester United's dominant run, does not necessarily agree.

He said: "I don't think the Premier League is boring, but you do look at other countries.

"People are always critical of what goes on in Scotland, where it's always going to be Celtic or Rangers.

"But for the last few years and maybe the next few years, they are going to say you can only see two or three teams winning it (the Premier League).

"I don't think that's boring for Chelsea, Manchester and Liverpool and those teams who are trying to win championships.

"But it just makes it very, very hard for us because every year, they are in the Champions League and every year, they are getting an extra £20million, £30million, £40million that the other clubs aren't getting.

"It's obvious they are going to get stronger and buy the bigger and the best players.

"The best example would have been last year: United won the league last year and before the week had finished, they had signed three players for £50million - and they had just won the league."