He said: "Newcastle changed too many things in a short space of time.
"They changed Mr Robson - that for me was the most important factor.
"When Mr Robson went, Newcastle slid down the table. It was inevitable. You need a good manager to motivate the players.
"I think they have that now, but they need to buy some players of the quality of four or five years before.
"It's a big club and has a huge fan-base - the biggest I have played in front of.
"Now they need the same again if they want to get back to the top."