"Major worry" refers to something that causes a significant amount of concern or anxiety. It is a term used to describe a serious or significant source of worry or stress. Full definition
The third major worry for me is everything around Arsenal is made about earning more money, not spending it. (justarsenal.com)
One major worry about the story was that it could be used to claim that WhatsApp is not secure, potentially pushing activists and other groups to use more non-secure messaging services. (businessinsider.com)
(Since 9/11, security risk has emerged as a third major worry.) (discovermagazine.com)