Pep Guardiola says Manchester City will have to adapt to the absence of Benjamin Mendy who ruptured an anterior cruciate ligament.
The 23-year-old French international left-back picked up the injury during Saturday's 5-0 Premier League win against Crystal Palace.
He is now expected to be out of action until at least April.
Mendy will undergo an operation to fix the problem, leaving Guardiola to consider altering his tactics, without the former Monaco man.
The City boss explained: "In the way he plays, the amount of times he goes up and down the sides, there is no replacement, we have to play in a different way," he said.
"Every player has his own qualities but there is no replacement in the world for the energy Benjamin has on the pitch.
"We have qualities in the other ones so we have to find the right balance."
With Sergio Aguero also ruled out of action with broken ribs following a car crash, Guardiola said his side will have to adapt.
"If we start complaining we'll never reach the step we want to get to. We are a strong team when we have those players but there are no complaints," he added.
"We have to overcome these situations if we want to become the team that people know it doesn't matter what happens to them.
"For big clubs it is all about how you react to these situations."