Gabriel, often referred to as Gabigol, joined Inter from Santos in a deal worth close to €30m just last summer. He was billed as the next big thing to emerge from Brazil and was as hyped as much as fellow youngster Gabriel Jesus prior to his move from Palmeiras to Manchester City.
But where Jesus has flourished since arriving in Europe, Gabriel has floundered.
He failed to establish himself at Inter, playing only sparingly in all competitions throughout the 2016/17 campaign, and will hope to get his career back on track in Portugal.
The absence of a language barrier may well help the 20-year-old settle better in Lisbon.