Swansea City striker Michu needs an ankle operation that will rule him out for up to six weeks.
The Spaniard, 27, missed the
2-1 loss to Everton
and was told he required surgery after undergoing scans on Monday and Tuesday.
"It's not good news," said Swansea manager Michael Laudrup.
“We will probably do something now in January and try to add something that we don't have in certain positions”
The Dane added: "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."
Michu has scored 28 goals for the Swans since joining from Rayo Vallecano in the summer of 2012, but has been hindered by ankle and knee issues throughout the current campaign.
The loss of the Spain international further dents Swansea's attacking resources, with winger Nathan Dyer likely to be sidelined until February after suffering an ankle ligament injury in the recent draw at Norwich.
Laudrup said the combination of the two injuries means it is likely he will look to bring in a forward during the January transfer window.
Among the players Swansea have been linked with is Liverpool striker Iago Aspas, who Laudrup actively pursued last summer.
"What has happened in the last couple of weeks has changed things," Laudrup admitted.
"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."
Swansea coach Alan Curtis said losing their star striker was a blow, especially during the busy holiday schedule, but added the prognosis could have been much worse.
"We were looking at two to three months," Curtis said.
"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."
Curtis also highlighted the fact that the Swans, who are through to the
last 32 of the Europa League,
have also had to do without Michel Vorm, Ashley Williams, Ben Davies and Leon Britton.
But he said he was confident results will improve once players return, allowing the team to focus a little bit more on the Premier League.
Swansea, who are 11th in the league, are next in action with their Boxing Day clash at Chelsea, travel to Aston Villa the following Saturday and then host high-flying Manchester City on New Year's Day.