Valencia reportedly allowed the 31 year-old to leave on a free in order to reunite with the club that gave him his professional debut in 2005.

Nani previously returned for a loan spell during the 2014-2015 season, netting 11 goals in 36 competitive appearances.

The UEFA EURO 2016 winner has failed to settle since leaving United with no more than one season spent at any of Fenerbahce, Valencia and Lazio, where he played on loan last term.

Sporting likewise struggled for stability in recent times, seeing a host of first-team players head for the exit after a training ground attack from fans at the end of last season.

It last month sacked Sinisa Mihajlovic after nine days in charge, installing former coach Jose Peseiro as his successor.