The Iceland camp in Russia have revealed Clarets winger Johann Berg Gudmundsson suffered a tear to a calf muscle in Saturday's 1-1 draw with Argentina.
But, encouragingly, Gudmundsson has not yet been ruled out of his country's first World Cup campaign.
Gudmundsson started in Moscow on Saturday as Iceland stunned Argentina in their Group D, but was withdrawn just before the hour - and just before Lionel Messi missed a penalty for La Albiceleste.
The 27-year-old has been monitored by the Iceland medical staff, ahead of Friday's group game against Nigeria, who are looking for their first points after losing their opening match to Croatia, in Volgograd.
“Johann Berg Gudmundsson has torn a muscle. It remains a question whether he will be fit but we’ll see on match-day,” Iceland's assistant coach Helgi Koldvidsson told a news conference today.
Iceland play their final group game against Croatia on Tuesday.