Manchester United secured qualification from the Champions League group stages on Tuesday with a 1-0 win over Young Boys at Old Trafford

Jose Mourinho accepts Manchester United must do better but feels it is unfair to compare the current side with the glory eras of the past.

United visit Southampton on Saturday in seventh place in the Premier League, 14 points behind leaders Manchester City and seven off fourth-placed Chelsea.

He says the game has "changed" so dramatically that it is impossible to repeat what has gone before.

"It's more difficult to buy players of a high level," said Mourinho.

"Before the smaller clubs were almost begging the big clubs: 'Get my best players. I need to sell.'

"I know absolutely we have to do better. But one thing is to do better. Another is to compare ourselves with what Manchester United was in the past because it is impossible."

The Tottenham example

In June 2006, Sir Alex Ferguson went to Tottenham to buy a replacement for Roy Keane, paying £18m for Michael Carrick, a member of Sven Goran Eriksson's England World Cup squad.

Two years later, he broke the club transfer record by paying £30.75m for Bulgarian striker Dimitar Berbatov, who had been Tottenham's top scorer for the previous two seasons.

Mourinho compares that situation to the one that exists now, where United can, theoretically, be interested in Tottenham skipper Harry Kane, but have no chance of completing a transfer for the England forward.

Mourinho said: "Is Manchester United, by its history and dimension, bigger than Tottenham? Tottenham is an amazing club but I think everybody would say yes. Can you buy Tottenham's best players? No.

"Football has changed. Can we go there now and bring Harry Kane here? Dele Alli? Eriksen? Son? No. So who is more powerful now? Them or us?"

'Crazy numbers'

The former Porto, Chelsea, Inter Milan and Real Madrid coach has spent £360m since he replaced Louis van Gaal at United in 2016.

Few of those signings can be regarded as successes and three of the most expensive, Paul Pogba, Romelu Lukaku and Alexis Sanchez, did not make the United starting line-up for Tuesday's injury-time Champions League win over Swiss side Young Boys at Old Trafford.

But, according to Mourinho, dealing in the modern transfer market is a hazardous experience.

He said: "You have no chance in the market unless you go to crazy numbers. Instead you go to the second level players where you still have crazy numbers, and where people say, and I agree, that's not what Manchester United is."

One way round that is to buy younger players and develop them, as United did with Cristiano Ronaldo and Wayne Rooney, who both joined United as teenagers and went on to become two of the most significant players in the club's history.

That policy "takes time", according to Mourinho, who feels United are a long way off being able to implement it.

There is also a suspicion at United that not all their rivals are playing by the rules. Mourinho's response to a direct question about how the world's richest club cannot simply buy players was a vague "you had one of the answers a few weeks ago". This was understood to be a reference to the financial fair play allegations made against Manchester City in Der Spiegel three weeks ago.

Sanchez 'very unlucky'

Evidently, United's situation would be far healthier if their most expensive players were able to reach their potential on a more consistent basis.

Alexis Sanchez has been a disappointment since moving from Arsenal in January and signing a contract worth £14m-a-year after tax.

Now the Chilean is out until the middle of January with a hamstring injury.

Mourinho said: "I don't like and don't believe in the word curse but he has had a very unlucky six months. We expect the new year brings better things for him."