Swansea says Michu is likely to be sidelined for six weeks, with the forward requiring surgery on his right ankle.
The 27-year-old Spaniard, who has scored 28 goals since joining from Rayo Vallecano in 2012, has been hindered by ankle and knee problems this season.
Manager Michael Laudrup said on Tuesday the operation is set to be carried out in the next week and Michu should be back playing in “around a month and a half.”
The loss of Michu further dents Swansea’s attacking resources with winger Nathan Dyer likely to be sidelined until February with an ankle ligament injury.
Laudrup says the injuries mean Swansea is likely to bring in a forward during the January transfer window.