Speaking to the club's website, sporting director Max Eberl spoke of his delight at the Foals' newest acquisition, saying: "We’re extremely glad that this transfer has gone through and we were able to sign Alassane despite a lot of competition from various other well known clubs."
Eberl went on to add: "Thankfully for us, he wanted to come to Borussia at all costs. He’s a versatile, quick and clever forward who has put his talent on full display in Ligue 1 and the Europa League."
Plea began his career at Lyon but it was after a move to Nice that the 25-year-old caught the attention of some of Europe's biggest clubs. Plea scored 44 times and provided 23 assists in 135 games whilst at Nice.
According to Sky Sports, Plea had been interesting Dortmund, who were also linked with Jean Michael Seri, now of Fulham.
News of the French forward's arrival comes after Gladbach officially confirmed that Jannik Vestergaard had joined Southampton. The centre back had spent two years with the German side and made 83 competitive appearances.
In a press release, Eberl praised the Dane's performances for the club, stating: "Jannik more than met expectations during his two years here after joining from Werder Bremen. We now wish him every success in the Premier League."