No. For all Android app users, and Apple version 2.2.0 and above, tickets will be available in your 'My Tickets' area even when you're offline. This means you can show them even if you're in an underground concrete jungle of a venue!
You will need to be connected at some point before to fetch your tickets, so ensure you open the 'My tickets' area of your app before you leave home. Once tickets are shown in the app, they will be available even when offline.
Alternatively, you can download the pdf versions of your ticket(s) as backup, please do this before you leave , to do this you will need to be connected to wifi/mobile data.