The Bafana Bafana midfielder had a contract until June 2013, but the two parties have parted ways with immediate effect.
Lierse say they have been trying since last year to extend Claasen's contract, but the 23-year-old and the club have failed to reach an agreement.
Claasen bid farewell to the Lierse fans in a statement posted on the club's website. "Dear Supporters, Lierse and I have today reached an agreement to terminate my contract. It was an honour to play for Lierse and their supporters. I want to thank everyone at Lierse for the past three years; coaching staff, players, back room staff, and the supporters.
"Lierse was the first club which gave me the opportunity to play at the highest level in Europe. I have had a lovely time in Lierse and have felt at home here. The three seasons that I've played here were not easy but in that period my colleagues and I have been able to enjoy the support of you supporters, and I'm unbelievably thankful to you all for that.
"I wish Lierse the very best for the coming seasons. I'm happy that I've been part of the Lierse family, and have contributed to some fine moments, such as my goal in the derby against Mechelen. It's now time to take a new step in my career.
"Lierse has done a lot for me, and I will always look back with pleasure and pride at my time in Lier. Bye, Daylon."
Claasen is reportedly now training with Everton in England.