Portugal midfielder Bernardo Silva will miss Thursday's World Cup qualifier away to Ireland due to "muscle issues", manager Fernando Santos told reporters on Wednesday.

Silva, who has been in terrific form for his club Manchester City this season and was instrumental in its Premier League derby win against rival, Manchester United at the weekend, missed training on Monday and was also absent on Tuesday.

"I don't count on him. He has muscle complaints. I don't think he has the conditions to go to this game. We think he will be okay for Serbia (on Sunday)," said Santos.

"He arrived tired, complaining, he has many games on him, and couldn't go to training, but he's recovering well and we hope and we believe he'll be able to play here with Serbia."

The game in Dublin against Ireland is crucial for Portugal, which trails leader Serbia by a point in Group A but has a game in hand.