The 27-year-old, who has scored 28 goals for the Swans since joining from Rayo Vallecano in the summer of 2012, has been hindered by ankle and knee issues throughout the current campaign.
The Spain international's frustrations have been clear to see, and manager Michael Laudrup has confirmed the player will need to undergo a procedure on his right ankle.
"It's not good news," said the Dane. "Unfortunately it has been confirmed that he will need an operation.
"It can be done in the next week and he should be back playing in around a month and a half."
Laudrup admits the combination of the two injuries means it is likely he will look to bring in a forward during the January transfer window.
Laudrup said: "What has happened in the last couple of weeks has changed things. We will probably do something now in January and try to add something that we don't have in certain positions.
"The numbers are a bit down and that is risky for the last four months of the season."
Among the players Laudrup has been linked with a move for is Liverpool striker Iago Aspas, who he actively pursued last summer.
"He is an interesting player but he is at Liverpool and they have injuries as well so that might not be possible," he added. "We are looking at other options."
Swansea, 11th in the Premier League, face Chelsea at Stamford Bridge on Thursday. They then travel to Aston Villa on Saturday before hosting free-scoring Manchester City on Jan. 1.
The club have received a boost after Welsh defender Ben Davies, 20, signed a new contract until 2017.
Laudrup said: "He's a very positive story. Not just for us but for Welsh football in general because it must be nice to see one of your own coming through.
"He came in and took his chance and the rest is history. He is doing well, playing for the national team and is still young."