The 18-year-old spent five months in England earlier this year and trained with the Premier League club's reserves as well as featuring for their Under-18 team.
Everton were impressed and have again offered Dier the opportunity to continue his development on Merseyside.
David Moyes could offer the defender a permanent deal at the end of the season if there are again signs of potential.
Dier was born in Cheltenham, but moved to Portugal at the age of seven before signing a contract with Sporting in April 2010.
Source: Team Talk
Source: Team Talk