The 25-year-old joined Inter last summer on an initial one-year loan deal and made an instant impact, scoring five goals in 36 Serie A appearances.
Inter, who finished third in 2018-19, will pay 20 million euros (£17.7 million) to complete the deal, La Gazzetta dello Sport reported.
(Reporting by Alasdair Mackenzie, editing by Ed Osmond)
