Depends what it is and the severity of it. You tend to find people who do meniscus damage dont get up unaided from that despite it generally being considered the lesser injury compared to an ACL injury.
you're entirely correct though in saying people can do their ACL and appear to walk normally immediately after if it's only a small tear. If it's completely snapped however then there's not a chance anybody is taking even a step and will require a stretcher. Both are essentially the same injury and will keep somebody from playing for 9 months yet visually will appear to be very different.
Players themselves might not even have a feeling of the severity, if it's fully snapped ligament you know straight away, I'm sadly speaking from experience on that but if it's a partial tear you could quite easily think it's not that bad.
All that is to say it's Impossible to speculate based on his reaction and apparent walking afterwards. Unless Rodri says he thinks it's fucked or he feels good, we wont have a clue until there's scans.
Praying it's simply a jarring.
Agreed. We can cope with a month or two if needs be so long as we dont pile more injuries on top of it, if it's any longer, that becomes a big, big problem.