Sinn Fein MEP Martina Anderson is set to replace Raymond McCartney in Stormont as the new MLA for Foyle.
A Sinn Fein source said Ms Anderson is the only candidate nominated to replace Mr McCartney, who is set to step down from the Assembly on Monday.
A Sinn Fein spokesman added: "A selection convention will take place tomorrow, the results of which will be announced afterwards."
The MEP is set to lose her job in the European Parliament at 11pm on Friday after the UK exits the bloc.
She previously help the post of Foyle MLA between 2007 and 2012 and was also the junior minister in the Executive Office.
Soon-to-be former MEPs the Alliance Party's Naomi Long and the DUP's Diane Dodds have also returned to the Stormont Assembly.
Raymond McCartney announced his decision to quit his Assembly role on Thursday saying the time was right to “pass the baton on”.
The former hunger striker has served as MLA for Foyle for the past 15 years.