Newly-promoted Monaco have signed 17-year-old striker Anthony Martial from Lyon for a fee of €5m.
Lyon said the decision to sell the France U-18 international was taken for financial reasons after the club had failed to find a buyer for Bafetimbi Gomis.
Martial joined Lyon as a 14-year-old and signed a three-year contract with the club in August 2012.
But he only made three starts for Lyon in the domestic league and one in the UEFA Europa League.
Monaco are expected to challenge defending champions Paris Saint-Germain, after marking their return to the top-flight with several highly-priced signings, including that of Colombian striker Radamel Falcao from Atletico Madrid.
But they will start the 2013/14 Ligue 1 season with a two-point deduction after they were penalised by the league following crowd trouble during a second division game against Le Mans.