Shaq's decision to pass on signing 'NSYNC after helping the boy band get off the ground is still tearing up Lance Bass' heart -- but he says there still would've been one major issue.
We got the singer at Villa Blanca in Bev Hills and our guy asked about Shaq coming thiiis close to signing 'NSYNC and the Backstreet Boys way back in the '90s.
Shaq's already said not signing the group is one of the biggest mistakes he's ever made, and Lance told us ... he couldn't agree more.