Sick Indian Runner

[MommaDuk]

I go out twice a day to check on my, currently small, flock. This morning I went out and didn't notice anything out of the ordinary and then when I went this evening my drake was sitting in the run, unable to lift his body up completely. His feet and legs are weak and he is only really able to move with the help of his wings to push him up. I thought I saw a bit of clear discharge coming from his nose (none from his eyes) when I came out before he started eating. His behavior otherwise is totally normal, he is eating and drinking well and I left him near food in front of water. Not sure what the problem is, any ideas/advice? I did notice that our rooster was picking on him, which is unusual because he's never shown any kind of aggression to any of our animals or us.