The the 27-year-old told the Telegraph he celebrated winning the title and the Capital One Cup too hard.
In a refreshingly honest interview, the Brazilian-turned-Spaniard said: "I got injured at the end of the season and then I went on holiday.
"Maybe I got out of my diet and when I came back I was not the way I was supposed to be. I was a little bit overweight.
"That affected my game."
Costa is right to take his share of the blame, after all he has scored just one goal in six Premier League games and missed the last three matches through suspension after his indiscretion against Arsenal.
His comments have shocked many fans and pundits that such a highly-paid athlete would allow his standards to slip.
But there have been a long line of players who battled with the bulge during their careers with it affecting some more than others.
Here we take a look at 10 other fat footballers.
10) Jan Molby
Liverpool's great Dane Jan Molby orchestrated the club's midfield in the 1980s and early 1990s. He also played 33 times for his country and actually became a cult hero because of his size. The fans' favourite started to go downhill in the aftermath of an injury sustained playing against arch rivals Manchester United 23 years ago this month. Unfortunately for Jan he would struggle to control his weight when injured and was often unable to train but retains legendary status amoung the Liverpool faithful and is well respected by fans of other British clubs.
What we're learning so far is that size literally isn't everything because the first two players on the list show you can still be top class and carry some timber. Widely regarded as one of the greatest strikers of all time, the thrice World Player of the Year saw his career start to stall in Milan where excess weight became a major issue and worsened on joining Brazilian side Corinthians. After retiring Ronaldo explained he had battled with hypothyroidism which made his achievements all the more remarkable.
8) Micky Quinn
Quinn still holds a record for scoring in consecutive games and is best summed up by the affectionate song fans used to sing about him: "He's fat, he's round, he scores at every ground." The former Portsmouth, Newcastle United and Coventry City striker never played international football but still managed to have a highly successful club career and ended his playing days with a fantastic record of 228 goals from 515 professional matches.
7) Jon Parkin
One of the lesser known names on the list but instantly recognisable to fans by his huge frame. Nicknamed 'The Beast' Parkin did not let his size hinder his hopes of being a professional footballer and he carved out a nomadic career in the Football League where he notched 161 goals in 522 games for 13 different clubs. He is still banging the goals in for Forest Green Rovers and talking about his weight problems in the past insisted: "It's something I have to put up with – it's just the way I am."
6) Tomas Brolin
The skillful Swede was a legend in his homeland for whom he played 47 times, but if truth be told Brolin's career was on the wane when he arrived in England and joined Leeds United. His excess weight contributed to a real slide in his final years in the Premier League where he also failed at Crystal Palace.
5) Neil Ruddock
Razor Ruddock as he was affectionately known actually ended his career as a direct result of his battle with the bulge. The big centre half had a distinguished career and even won an England cap. His weight did not impact on his playing style as an uncomprimising centre half. But when his Crystal Palace contract was terminated by mutual consent amid concerns over his weight and fitness and he completed just 15 games for Swindon before a similar scenario reared its ugly head, he know he had had his day.
4) Benni McCarthy
The once prolific and Champions League winning South African's career was one fraught with weight issues. It all started back in 2009 when he clashed with Blackburn Rovers manager Sam Allardyce over extra fitness training. He was later left out of South Africa’s 2010 World Cup squad because of fitness problems and it culminated in being fined and eventually dumped by West Ham for being overweight after making just 11 appearances following a £3.5 million move to East London during Gianfranco Zola's tenure.
3) Neville Southall
One player whose weight certainly did not hamper his career. Like Molby, Southall became a cult figure for his brilliant performances despite not fitting the stereotypical image of a top level sportsman. The legendary goalkeeper made almost 600 appearances for Everton and had 92 caps for Wales. Was and will always be remembered as one of the best goalkeepers of his generation.
2) Adel Taarabt
According to then Queens Park Rangers manager Harry Redknapp the Moroccan-born playmaker was "three-stone overweight" when they were together at the club. Taarabt refuted Redknapp's allegations and hit back by showing the media his physique which while not being particularly impressive was certainly not as bad as the manager had implied. The relationship was beyond repair after that and while Redknapp was relegated and hasn't had a job in management since, Taarabt moved to AC Milan where he scored four goals in 14 games and is now at Benfica.
1) Diego Maradona
Arguably the best footballer that has ever lived, Maradona's weight fluctuated during his career as he struggled with various off the field problems. When he failed a drugs test at the 1994 World Cup, the Argentine legend claimed the prohibited substance was in a weight loss drink. His weight has fluctuated in his retirement but he will forever be remembered as one of the all-time greats, if not the greatest, so his issues did not hold him back in any way.