Manchester City midfielder Kevin de Bruyne will be sidelined for four to six weeks with a hamstring injury, says manager Pep Guardiola.
The Belgium playmaker, 29, suffered the injury during Wednesday's 2-0 Premier League win against Aston Villa.
His absence will start with Saturday's FA Cup fourth-round tie at Cheltenham.
De Bruyne could miss up to 10 matches, including the Champions League last-16 first-leg tie with Borussia Monchengladbach on 24 February.
"The doctor said after reviewing the scan Kevin will be out for four to six weeks. It's a big blow, but we have to move forward," said Guardiola.
"I'm not saying anything that anyone doesn't know - it is unfortunate for him and for us and we have to find a solution because everyone in their own life is struggling in the situation we are living in and we have to adapt."
City are unbeaten in 16 games in all competitions, including wins in all their past nine matches, and are second in the Premier League, two points behind Manchester United, but with a game in hand.
As well as the FA Cup tie at League One Cheltenham Town, De Bruyne will also miss Premier League matches against West Brom, Sheffield United and Burnley as well as games against fellow title contenders Liverpool on 7 February at Anfield and Tottenham at home six days later.
He could also be absent for the home league game against Arsenal, the Champions League tie against Monchengladbach and the Premier League encounter with West Ham. City are then scheduled to play a derby game against Manchester United on 6 March.
Guardiola said his players are having to play too many matches and are picking up injuries as a result.
"To demand they are fit for 11 months, playing every three days, is impossible," said the Spaniard.
"With this amount of competitions, the body says 'it's enough'. The players don't want to get injured but it's no secret.
"When we demand five substitutions, it's for this reason. Why can we do it in the FA Cup but not the others? I'm not just saying it because it's Kevin, it's too many games and competitions and in the end the players suffer."
- You can stream five fourth-round games live on the BBC this weekend, including Liverpool's trip to Manchester United. Find out more here.