Members of Leyland Albion Football Club stayed at the Hotel Oasis Park in Salou as part of the tournament.
The holiday was booked through Absolute Travel and Tours and funded by the club for the members attending, with most of the players there aged around 12, however a number of parents went along and paid for themselves.
Among those unwell was Harry Newbury, nine, the son of club secretary Helen Newbury, and football coach Neil Matthews and his wife Joanne.
The club arrived in Spain on May 23, with Harry starting to display symptoms a number of days after arrival, including vomiting and stomach cramps.
M6, M61 and M55 delays in Preston due to Blackpool Air Show and Lake District holiday traffic
Lanes reopen after car crash on M6 brings Preston motorway traffic to a halt with severe delays expected
Driver caught 'snoring merrily away' on the M6 near Bamber Bridge with full-beam headlights and engine running
Thunderstorms and heavy downpours of rain predicted to hit Lancashire as Met Office issues yellow weather warning
Two Preston men arrested after serious assault near Harris Museum
He was so poorly he missed out on one day of football.
Coach Neil, 41, and his wife Joanne, 42, both began vomiting and having diarrhoea after arriving in Spain, and both are still suffering from loose stools and a lack of appetite.
Specialist international personal injury lawyers Irwin Mitchell are now investigating after being contacted by several holidaymakers.
Neil and Joanne told Irwin Mitchell they had reported their illness to hotel reception but felt that it was not being taken seriously.
They suspected that food was undercooked after being asked if they wanted their chicken cooked medium or well done, and also noticed the crockery was dirty.
They noticed that some of the food was uncovered and appeared to have been left out for some time.
The pair said the pool area was littered, and the toilets around the poolside were not very clean.
Neil said: “We flew out to Salou as part of a large party to enjoy a football tournament, and instead we were very unwell and miserable.
“The football club spent three years fund-raising for this trip and it was completely ruined for some of us.
“Now we are back home, we are still not feeling one hundred percent and really need answers as to why this happened and whether or not it could have been stopped from happening.”
Clare Pearson, specialist holiday illness lawyer at Irwin Mitchell, said: “Several holidaymakers have asked us to investigate what caused their illness at the Oasis Park in Salou.
“We’ve heard reports from our clients that their illness may have been part of a wider illness problem as several other guests were also known to be ill.
“Sadly our clients have not got their summer off to the best start as their well-earned holidays have been hit hard by gastric illness which has continued to affect them on their return home.”
Absolute Travel and Tours were contacted for a comment.