Gregoire Haemmerle, head of advisory for France, Belgium, Luxembourg and Switzerland at UBS, is set to take up a post at Citi, the source said, adding that Pierre Drevillon, a managing director in the corporate advisory unit, is set to depart.
Haemmerle joined UBS in 2015 from JPMorgan (JPM.N), where he spent 19 years, including as head of investment banking for France.
UBS, which recently poached star banker Marco Illy from Credit Suisse (CSGN.S) to head up its Swiss investment bank, declined to comment.
Citigroup did not immediately comment.
Reporting by Lawrence White, writing by Emma Rumney, editing by Silvia Aloisi and Louise Heavens