Former Manchester United assistant manager Carlos Queiroz has said that there have been too many changes at the club since Sir Alex Ferguson retired, and has accused the club of panic buying during the last few transfer windows.

Louis van Gaal signed 19-year-old Anthony Martial for an British record initial fee for a teenager of around £36m on transfer deadline day, and British record signing Angel di Maria departed for Paris Saint-Germain this summer after failing to settle into life at Old Trafford.

Queiroz, who spent five years as Ferguson's right-hand man at the Red Devils, says that the Scot's successors David Moyes and Van Gaal have made crucial mistakes in how they have run the club since Ferguson stepped down.

"The foundation of Manchester United's success was based always on trust, confidence, continuity – I think that there have been too many changes that disrupted the continuity and tradition of the club," he told The Guardian.

"There was nothing wrong with building the future based on the principles that were already inside Manchester United created by Alex Ferguson, that was the right direction. I understand that after Alex... the complexity of the transition was not an easy task.

"I have great admiration and respect for Louis [van Gaal] and David [Moyes], they are great coaches that I admire but I think that they made some critical and crucial mistakes in the transition from Alex."

The current boss of the Iran national team highlighted Moyes's changes to the coaching staff at the club, and said that despite the money that United have been spending, the club is now devoid of such stars that it boasted in the past.

"I hope and expect this season that Manchester United is able to not only compete, to win but to win in style because that is what Manchester United is about, winning with style and entertainment.

"We also want to see the players shining. Great players like [George] Best, [Paul] Scholes, [Ryan] Giggs, [Roy] Keane, [Ruud] van Nistelrooy – where are they? Where are the stars of Manchester United?

"It was always about creating players. Now it is the opposite. I saw Di Maria and some games, he looked like he has never played football. There is panic buying. You can still make wrong decisions but we never made panic decisions when buying players."

After leaving United in 2008, Queiroz managed his home nation Portugal for two years before taking over at Iran in 2011, leading them to a place at the 2014 FIFA World Cup.