LONDON -- Mauricio Pochettino has warned Tottenham's best academy players that it has never been harder for them to break into his first team.

Since moving to Southampton five years ago this week, Pochettino has established himself as a champion of youth but he believes Spurs' youngsters need to be 10 or 15 percent better now than when he joined the club from St. Mary's in May 2014.

The Argentine put faith in Harry Kane, Ryan Mason and Andros Townsend during his first season at Spurs but, this week, he sent the two most talented academy graduates at the club on loan to the Championship.

Marcus Edwards, 19, has joined Norwich on loan until the end of the season, while U.S. international Cameron Carter-Vickers, 20, will spend the rest of the campaign at Ipswich, having been recalled from Sheffield United. Georges-Kevin Nkoudou, 21, has also joined Burnley on loan.

Asked if it has never been harder for a young player to break into his team, Pochettino said: "Yes. If you were seven out of 10 four years ago, you were going to have the possibility to play.

"But now we have said to them that they need to be an eight or an eight-and-a-half. That is more demanding for them.

Mauricio Pochettino has become more demanding of Tottenham's academy players. Reuters/Darren Staples

"We have built a very strong squad and a very strong starting XI and it is difficult to get the possibility to play. Now the level is higher and higher every season. Now it is not only about quality. It is not only about showing something good.

"You need to show quality, mental strength, physical condition and everything if you want to get the possibility to play in the first team. In the last two years we have been competing for the Premier League title, for the top four. Now the demands are higher than before."

Pochettino insisted that Carter-Vickers still had a long-term future at the club and urged winger Edwards, whom he has previously compared to Barcelona's Lionel Messi, to prove himself with the Canaries.

"Marcus is a very talented player but he needs to move on, to step up," Pochettino said. "An opportunity has arrived at a very good club like Norwich and it's a great opportunity for him to step up, move there and try -- in three-and-a-half months -- to get more mature and to compete.

"He now has the possibility to be a man, to be more mature and to help himself to achieve all that we believe he can achieve. It's a process and for us he must be positive."

Despite admitting it is getting harder for academy players to break through, Pochettino said he would always make space in his squad for youth.

"Rather than have 25 professionals, I would rather have 20 or 21 and give four or five places to younger academy players. Because if we have 25 senior player it is so difficult to find the space and provide the youngsters the space to play," he said.

"If you save money like we did at Espanyol by signing three or four players less, you can invest more in the rest of your squad, academy and can provide the [youngsters with the] possibility every week to train with the first team and possibility to play because of injuries or some suspensions.

"When we arrived here three-and-a-half years ago we had 33 professional players. How do you provide younger players with possibility to play?

"Of course the credit for Harry Kane, Harry Winks and every young player is about everyone. It is about people who believe [in them] at 15, 16, 17 and help you and provide the tools to get in the first team. That is always why I share the credit when some player arrives at the first team."

Asked if there was a vacancy for a speedy wide-man in his squad, Pochettino told a news conference: "Our football is playing football. It is not counter-attack. It is not transition.

"I think Usain Bolt is free? I think he is available. But his dream is to play at Manchester United. I feel sorry for him because he is a Man United fan. It is impossible to be faster than him!"

Asked directly about rumoured Bordeaux recruit Malcolm, the Spurs manager -- who never comments on transfer speculation -- said: "He has been linked with different clubs. I don't want to speak about players that are in other clubs."