Midfielder Andrew Hall was brought in for questioning over the killing of 15-year-old Megan Leigh Peat, who was stabbed to death on Saturday night.
Newspaper reports claim witnesses saw a teenage boy leaving the half-term party in Ampthill on Saturday covered in blood.
Hall is reportedly in hospital receiving treatment for a near-severed finger; detectives have yet to begin questioning him about the events of the night.
Paramedics were called to the scene at 1.30am but were unable to save Megan's life. The results of the post-mortem have yet to be disclosed.
Luton-born Hall, who turned 18 in April, played for Stoke's under-18 side last season and scored the goal that put them into the fourth round of the FA Youth Cup.
A Stoke City spokesman said: "The club are not prepared to comment at this stage other than to say that the thoughts of everyone here are with Megan’s family at this tragic time."
Megan's friend Georgie Dymock told The Sun that Megan had been seeing Hall since last year.
"She and Andrew were on and off for about 10 months. They met through friends. She was well happy," she said.
The party was apparently held in a cul-de-sac at the home of a boy whose parents were away, according to neighbours, though it is not yet clear who was in attendance: "I heard the owners were on holiday. I heard the son wasn’t even there and lent his keys to a friend,” one neighbour told The Sun.