Now United have entered the fray, with David Moyes keen to save his side’s season.
Costa has hit a staggering 23 goals in 21 appearances this season, but could be on the move thanks to a £32m release-clause in his contract.
The Red Devils are rumoured to be ready to make one of two significant signings in the coming weeks, with a top class attacker on Moyes’ wish list thanks to Robin van Persie’s injury woes and uncertainty surrounding the future of Wayne Rooney.
Costa is seen as an ideal marquee buy, and the sort of player that could create a sense of optimism at Old Trafford after a poor opening half of the season.
United are believed to have had scouts in attendance for Atletico’s last game, with the striker and his team-mate Koke thought to have been the subject of the visit.
Costa was born in Brazil, but is set to represent Spain at the World Cup after securing citizenship in his adopted nation.