Tony McCarroll, 53, was one of the founders of the group, which caused a sensation last week when its warring frontman brothers Noel and Liam Gallagher announced it was making a comeback with a string of 2025 stadium gigs.
The percussionist has now told The Sun about his regret he had a bust-up with Noel, 57, before he was kicked out of the band in 1995 - leading to him being replaced by Alan 'Whitey' White.
He said: "There was tension in the band - not only with me. The band was a tough place to be sometimes.
"I remember (a) Paris gig - drinking was involved, I ended up arguing with someone in the room next door to Noel and the next day Noel said, in front of the sound crew and everyone, 'Don't ever keep me awake at night or I'll sack you'.
"I'd had enough. I'd had enough of the poking each other and this, that and the other, so I swept the kit out the way and went up to Noel - right up to his face - and said: 'Don't you ever talk to me like that'.
"It was probably the biggest mistake of life."
Tony was asked to leave Oasis, with his replacement Alan White, 52, continuing with the group until 2004.
He then filed a lawsuit against Oasis, alleging he was "unlawfully expelled from the partnership" and was owed royalties of £18 million as part of his five-album deal with Creation, the label that signed the band.
Tony eventually accepted an out-of-court settlement of £600,000 in March 1999 as well as giving up all claims for future royalties.
He added he is convinced Noel and 51-year-old Liam's mother Peggy, 81, helped them reunite ahead of next year's tour.
He said: "I've always, always, always, always said it, that they would get back together.
"It's not like they're two estranged friends, if you like, they're brothers.
"I reckon Peggy being the old Irish lady that she is, is banging their heads together."
He added about his hope he will get a call to join the group on the road next year: "I don't know if I'm going to be asked, if there's a whole thing going on that I don't know about."