Newly-promoted Monaco have signed 17-year-old striker Anthony Martial from Lyon for a fee of 5million euros.
Lyon said that the decision to sell the French under-18 international was taken for financial reasons after the club had failed to find a buyer for another striker, Bafetimbi Gomis.
Martial joined Lyon as a 14-year-old and signed a three-year contract with the club in August 2012.
But he has made only three starts for Lyon in the domestic league and one in the 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 season on minus two points after they were penalised by the French League following crowd trouble during a second division game against Le Mans.