The Spaniard, who last played a competitive game 428 days ago, was the Red Devils' No1 for 12 years.
De Gea had a new contact at Old Trafford pending after agreeing to cut his wages from £375,000 to £200,000 per week.
But the club asked him to hold off on signing the deal as they mulled over their options.
Man Utd eventually brought in Andre Onana and the 33-year-old's exit came to light on his wedding day as he tied the knot to wife Edurne Garcia.
De Gea has supposedly had offers to return to football, with the likes of Newcastle, Nottingham Forest, Real Betis and Saudi Arabian clubs all interested back in January.
But the goalkeeper chose to stay without a club.
This summer, he has reportedly been in talks with Italian clubs Genoa and Fiorentina.
However, various claims say he has turned both down after they failed to match his wage demands.
TEAMtalk report that De Gea wants a £5million-a-year contract, which would see him earn £80,000-per-week.
His "unrealistic" wage demands are out of Genoa's budget and Fiorentina were only able to give him a £4m-a-year contract.
De Gea has been staying in shape, regularly posting videos of him training on social media.
