Pep Guardiola explains why Sergio Aguero and Gabriel Jesus can't play together for Manchester City
Both strikers have been in fine form as City have swept all before them at home and away on their way to the top of the Premier League and into the last-16 of the Champions League.
Guardiola used the pair together to devastating effect but Mendy's knee injury, which is likely to keep him out of action until April, has forced him to change tack.
As a result the Spaniard is having to choose between the two, a decision Guardiola reveals is his hardest selection call right now.
"Both have different qualities - they deserve to play," he said in his pre-match press conference ahead of Tuesday night's visit of Feyenoord. "They have a lot of games and they have to be ready. It is the toughest decision."
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He added: "When you have Mendy, he can play wide and the winger can go inside. Fabian Delph cannot do that. Without Mendy, Leroy Sane has to go wide, which is why they don't play together. Sergio after the crash, he was fit. He is fit. For me he is so tough. So is Gabriel."
With City's progression already secured Guardiola is expected to ring the changes against Group F's last placed team and hinted highly-rated youngsters Phil Foden and Brahim Diaz could be handed full debuts against the Dutch side.
"They are two young players training this season. What I saw in the pre-season, the training, the World Cup, they are ready," he added. "Here in the high level we try and help the young players. They've shown me the same we saw when they played in the second and third team. The skills and quality are there.
"We can help them with speed because the lack of time is higher so Phil has to fight duels against Kevin De Bruyne, against Fernandinho, against David Silva. Every day is a step to improve.
"Years ago, people had more time to think. Now it is reduced. Everything is quicker. The players are faster in all senses, physically and mentally. I said in pre-season, those guys will train with us all season. They have to be ready. Sometimes the manager makes a surprise."