More Concise:
* The weak puppy struggled to stand.
* The puppy was too weak to stand properly.
More Descriptive:
* The weak puppy wobbled precariously on its tiny legs, barely able to stand.
* Its legs trembled, and the puppy barely managed to stay upright.
Adding Context:
* The weak puppy, barely able to stand, whimpered pathetically.
* The weak puppy, barely able to stand, looked up at its mother with pleading eyes.
Choose the option that best fits the context of your story or description.