Oil producer Tullow Oil Plc (TUWLF) said there was a potential issue with a storage vessel at its flagship Jubilee field in Ghana, sending shares down more than 7 percent on Thursday morning.
The company, which is expecting a second field in Ghana to begin production this year, said it had taken additional measures to monitor part of a turret bearing in its floating storage and offtake vessel.
"The implications are that the turret may require maintenance that results in an unscheduled shut-in," RBC Capital Markets analysts wrote in a note to clients.
RBC expects Jubilee to contribute nearly half of the company's production in the first half.
The company said it was working with the original manufacturer of the bearing, and that oil production at the field was continuing as normal.
Shares in the company were down 7.4 percent at 177.2 pence on the London Stock Exchange at 0858 GMT, making them the largest losers on the FTSE mid-250 Index.
(Reporting by Mamidipudi Soumithri and Karolin Schaps; Editing by Sunil Nair)