Michu is set to miss at least the next six weeks after scans on Monday showed he is likely to need an operation, according to Swansea coach Alan Curtis.
The Spaniard was forced to sit out the Swans' 2-1 defeat to Everton after the re-emergence of a recurring ankle injury.
And Curtis says the Welsh side will decide on Tuesday whether the former Rayo Vallecano man will require an operation.
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"Hopefully we're looking at something maybe around the six-week mark [out].
"It will be a blow obviously to lose him for that length of time, but possibly we were looking at two to three months.
"But to be fair to him it's something that needed to happen, because he's been struggling with his knees and his ankles.
"It's interrupted his training and he's missed a fair chunk of game-time this year.
"So we've missed him, likewise Nathan Dyer we've missed a lot, and Michel Vorm had a cartilage operation midweek.
"Ashley Williams has been out, Ben Davies has been out, Leon Britton has been out - some big players for us that have missed a fair portion of the season.
"That allied to the European football [Swansea's Europa League campaign that has seen them qualify for the last 32], if we can get some of these players back we can concentrate a little bit more on the [Premier] League and I'm sure results will improve."