There is one verse of the Qur'an that mentions lions specifically, but it uses an unusual word (قسورة rather than either ليث or أسد). It is used in Surah Muddathir:
- 74:49 - Then what is [the matter] with them that they are, from the reminder, turning away.
- 74:50 - As if they were alarmed donkeys.
- 74:51 - Fleeing from a lion?
So it is describing that a lion is an animal to be feared, with the rejecting non-Muslims fleeing from the message, like donkeys fleeing from a lion.
In the hadith there are many mentions of lions. In particular, the Prophet's uncle Hamza ibn Abd Muttalib had the title of the Lion of Allah (أسد الله) according to wikipedia. Clearly, this is in the context of Hamza being amazingly brave; so it is being used in the sense you refer to it.