David Bergin, 30, bet against his team. Originally from England's north west, Bergin watched United home and away, week in week out, before the 2005 Glazer takeover. Life for him was never the same after that and he's not been to Old Trafford since 2005. Many United fans feel the same.
Instead, he started watching Rayo Vallecano, the third biggest team in Madrid. He'd fallen for this mistress while in Madrid en route to see United play in Valencia in 2001. He started going to games when he could and was welcomed into the Vallecas fold. He travelled to away games the length and breadth of Spain to watch Rayo in the third and second division. From Irun on the Basque-French border in the north, to Las Palmas in the Canaries off the coast of Africa.
In 2011, he moved to Madrid so that he could watch his adopted team more often. He chose a good time, for Rayo were promoted to the top flight, despite boasting a team of young players, several of whom had never played at that level before. Players like midfielders Javi Arribas and Michel, forward Piti and full-back Tito in two seasons with Rayo went from the third division and away games in front of 1,000 to playing Barca and Real Madrid in front of 80,000.
Despite players not receiving their agreed salaries after a dispute with a former club president, Rayo, whose coach Jose Ramon Sandoval had never coached above Spain's fourth division until 2010, reached the giddy heights.
The 43-year-old coach worked a miracle, getting Rayo out of the second division in his first season at that level and while his players threw him in the air to celebrate, his feet remained firmly on the ground - as they could only ever be in Vallecas, a working class barrio immediately south of central Madrid. He has continued to excel this season and new Vallecas resident Bergin has seen it all. In keeping with the club's left-wing ideology, he made a Che Guevara-style tee-shirt for Sandoval and presented it to him. The Rayo coach waved it around on the pitch and then decided to make a gesture of his own. He got a Rayo shirt and had 'David' printed on the back.
"It's the perfect triangle of fans, manager and players who understand each other," says the thrilled Bergin.
Rayo fans shout 'Manchester' when they see him and consider him one of their own. For the recent game against Real Madrid, the game where Jose Mourinho praised the febrile atmosphere in Rayo's three-sided 15,500 capacity stadium, Bergin won a prize to stand with the players for the pre-match photo. Feeling cheeky, he then stood at the end of the Rayo team as the Madrid players came past to shake their hands.
"Pepe had piercing eyes and hugged me, Higuain tapped my backside when he saw my Guevara t-shirt and Cristiano Ronaldo smiled and winked when I said: "Manchester United siempre (always)."
With his knowledge of Spanish football, Bergin bet that Athletic would beat United at Old Trafford at odds of 7/1.
"I've watched Athletic play twice this season and know how good their players are," he explained. "I wasn't surprised when they won."
He collected his winnings, though it wasn't a great sum: having trained as an English teacher, he is now looking for work against a backdrop of 23 per cent unemployment in Spain. It was, however, enough to cover a trip to watch Rayo at Espanyol on Sunday.
Not for him a train or plane - that is just too expensive - but a bus; when the one organised by Rayo's fans was cancelled after numbers halved following a short-notice switch to a Sunday midday kick-off, his only option was an eight-hour night bus from Madrid to Barcelona with 10 other Rayo fans. One of them is an 80-year-old lady who follows them everywhere.
He arrived in Barcelona and went straight to the stadium without a ticket; with Espanyol trying to charge away fans €40, they instead bought €20 tickets in the home end.
When 50 Rayo fans then presented those tickets at the hitherto empty away end, what choice did the police have but to let them in? One in the eye for Spanish clubs who attempt to profit at the expense of away fans.
His team were beaten 5-1 and he spent the day in Barcelona before catching another overnight bus back to Madrid. Rayo are still a creditable 10th and just four points off a European spot with 12 games to play - though the top 15 teams are all in contention for those sought-after remaining European places.
Bergin will be in Bilbao on Thursday to watch United at the San Mames. He doesn't have a ticket: a lot of United fans have refused to pay €92 and will either not go or try to buy a cheaper ticket on the day.
His head knows that Athletic are capable of destroying United once again, though his heart desperately wants United to rediscover their old European form against the brilliant Basques.
That is, the part of his heart which hasn't been lost irrevocably to Rayo.