The Hebrew says his loin, or basket, singular
A dictionary set of options includes:
to toast, to roast [we-future]
to be toasted, to be parched [he-past; masc-sing-present; we-future]
to be disgraced [masc-sing-present; we-future]
easy [adj-fem-sing]
despicable, dishonorable, trivial, trifle [adj-masc-sing; adj-fem-sing]
Since this is poetry, it could be translated something like "the Lion was old and sick (is that a hey?), and his loin (intention) was filled with treachery.
Amazing Grace is usually translated with נִקְלֶה as "a wretch":
"חסד מופלא, כמה מתוק הוא הקול, אשר הציל אדם נקלה שכמותי"