Malta international midfielder Matthew Guillaumier joined Polish top division side Stal Mielec. He signed a two-year deal with the club retaining an option of extending the deal by another season.

A product of St. Andrews, Guillaumier made his senior team debut at the age of 15 in the First Division. He had a spell with Italian side Empoli in the latter part of 2013 before returning to Malta to play on a more regular basis with St. Andrews before the turning out for the Malta Under-17 national team in the UEFA Under-17 Championship finals in May 2014. He moved to Birkirkara in January 2016 but joined Hamrun Spartans in 2020. With the Spartans, he won two championships in three years and was voted Footballer of the Year twice.

During season 2021/22, Guillaumier had a six-month spell with Siena in the Italian Serie C.

Last season Stal Mielec placed eleventh in the Ekstraklasa out of the eighteen teams.