Barcelona's players shared their concerns with manager Hansi Flick about his tactics in the wake of their 4-0 thrashing by Atletico Madrid in the semi-finals of the Copa del Rey. The result leaves the Blaugrana with a mountain to climb ahead of the second leg of the tie at Camp Nou in March, and the players have called on the manager to make changes to his system.Barcelona have been in impressive form again this season under Hansi Flick, topping the table in La Liga, qualifying for the knockout stages of the Champions League and beating Real Madrid to lift the Spanish Super Cup in January. However, their hopes of retaining the Copa del Rey unravelled on Thursday night as they were beaten 4-0 by Atletico in the first leg of their semi-final. Diego Simeone's side ruthlessly exposed Flick's infamous high line and gave the Catalans a tough time. A difficult night for the club was compounded by a Pau Cubarsi goal being ruled out for offside after an eight-minute VAR delay, while Eric Garcia was sent off late on as Flick's side finished the game with 10 men.The result led to some soul searching on the training ground the following day, according to The Athletic. Flick had his say and questioned the players' mentality and intensity, while there was also criticism of the coach. Barcelona stars revealed their concerns to their manager about his tactics, claiming his high line "was not the best idea, as conditions were not right for that in their eyes". The players feel it's incredibly hard to apply his style when key players such as Raphinha and Pedri are absent. Both players were ruled out of the match due to injury and were badly missed by Flick's side. While Barcelona's players do not want to abandon Flick's approach, they do want "more pragmatism around key games and against certain opponents, as well as greater adaptation to the players available".Flick spoke about his team's defeat after the game and admitted Barca had been taught a lesson by Atletico. He told reporters: "We didn't play very good in the first half as a team. We had too much distance between everyone. We didn't press how we wanted. In the first 45 minutes or more, we got a lesson. Sometimes it's good in the right moment. Maybe today was the right moment. I am still proud of my team, maybe not today in the first 45 minutes, but across the whole season. When you see how many injuries we have all season, how we adapt...Today was a heavy loss but I am proud of my team. We will come back. We need to start from the beginning [of games]. When you see Atlético players, they had more will, more hunger. And this is what I want from the first minute. We didn't show that in the first half. We have the second leg. We will fight for that. If we are able to win each half 2-0, this is our goal. We need our fans in Camp Nou and we will see what happens."Add GOAL.com as a preferred source on Google to see more of our reportingBarcelona have also been left furious by the decision to disallow Cubarsi's goal after a farcically long VAR delay. The defender netted early in the second half and his strike would have made it 4-1,  giving Barca hope of trying to find a way back into the game. The lengthy delay was due to the failure of the semi-automated offside technology, forcing VAR officials to draw the lines manually. Barcelona midfielder Frenkie de Jong did not hold back in his criticism of the situation. He said: "In the offside photo, you can't even see the contact with the ball at the moment Fermin shoots. Later, another image came out where it was clear the defender was a meter behind Lewandowski. This is very strange, it’s a scandal."The second leg of the tie is not due to take place until March 3, giving Flick plenty of time to get his injured players back. In the meantime, the German coach will hope to see a response from his players on Monday when they resume their title challenge away at Girona.