The 24-year old gloveman is now a permanent Parkhead fixture after spending the last two seasons on loan following his shift from Newcastle United this summer.
Forster is now preparing for the upcoming Champions League qualifiers against Finnish club HJK Helsinki, which begin on August 1 at Parkhead, and he insists that a steady defensive unit at the back will assist the team in moving through to Europe's premier club competition proper.
"It's important to have a settled back four as it affects me as a goalkeeper," said Forster.
"When we went on a great run last season it was almost the same 11 players who played every week.
"It's most important to have a solid back unit and spine.
"This is as big a game as I've played in at Celtic.
"Every player in the changing room wants to be in the Champions League."