Rabbits can definitely get goop like “sleepy” stuff that you may notice from time to time (that’s normal), but if it continues or worsens, it can mean an infection. (in the eye or in an upper tooth root). You can try and feel around the outside of the upper cheek to see if you feel a difference on that side, as tooth root infections can also sometimes cause swelling or an abscess, then vet care would be needed in that case. 

Do the eyelids on that eye look a bit red, or if you lift up the lid, is the white part of the eye redder than the other eye? Sometimes, an infection can cause a slight smell. You’d have to put your nose right up to it to smell it.

So just keep an eye on it, and if it does seem like an infection, then vet care with antibiotics may be given because rabbit eyes have a very difficult time healing on their own due to the fact rabbits don’t don’t blink. The dryness prevents healing. And then an ulcer can develop which can be even harder to heal (Been there, done that!). But don’t worry, it’s not like you would have done anything wrong. A vet visit isn’t a reflection of how well you take care of your animals. It just happens from time to time even in healthy animals.

Keeping my fingers crossed though that it’s nothing serious and it was just some goop