Speaking to Sky Sport after the game, Jashari was blunt in his assessment of a performance he felt fell short at both ends of the pitch.
"I think we lacked something both with the ball and without it, and then you concede goals and don't score," he said.
"We haven't created our own chances the way we train for it, we have to do more. For the next games we have to do better."
The 23-year-old, who joined Milan from Club Brugge for around €34 million last season after being voted the best player in Belgium's top flight, called on the squad to hold itself accountable regardless of results.
"We're players of a huge club, we all have to take responsibility together," he said. "Whether we win or lose we have to accept it, and winning is the most important thing at this club. We have to improve every day — obviously we also saw positive things today, but in the final third we have to improve a lot. It's not good to be so predictable."
Asked whether such struggles were simply part of adapting to a new project under Amorim, Jashari pushed back on the idea that the coaching setup was to blame.
"I've already said we have to believe in this project, but that alone isn't enough," he said. "We have to be aggressive — if we're switched on and there's the right spirit, then we can do well. It's all on us, not on the project."
On Milan's tendency to play short passes rather than look for balls in behind, Jashari acknowledged his own preference for a more direct game, while stressing the issue went beyond his individual role.
"Everyone knows I like to play the ball behind the defenders — in some games that option isn't there and we have to create it better," he said. "It's not just about me, it's about all of us. It's good when there are more options; in every situation you need more options to create."
Pressed on whether he had been too passive for Benfica's opening goal, compared with his form for Club Brugge or Switzerland, Jashari took the criticism on the chin.
"We have to improve as a team — the move for the first goal came from a lost ball, and I chased back," he said. "I should have been closer to my teammate."