The Big Ten’s continued pursuit of four Pac-12 schools is leading to concern that another round of expansion could collapse the Pac-12, industry sources tell CBS Sports. This as Big Ten commissioner Kevin Warren continues to seek an offer from Amazon, or potentially another partner, for additional Big Ten football media rights revenue. An offer deemed substantial enough would likely convince Big Ten presidents that California, Oregon, Stanford and Washington would be valuable additions to the league from the Pac-12. That figure is believed to be less than $100 million annually. If the Big Ten makes such a move, it would almost certainly increase the likelihood the Big 12 is…