There's a short story titled The Ruum (Arthur Porges 1953) that has the main elements you describe. The 'Ruum' is the 'ball' but is described as 'bloblike' in the Wiki synopsis. Also, the story takes place on Earth, not an uncharted planet.
The Ruum (shape-shifting, indestructible robot) is accidentally left on Earth by aliens during the age of dinosaurs. It's job is to collect different species of animals weighing 160 lbs (+/- 15) and preserve them in suspended animation for later retrieval.
Jim Irwin, a uranium prospector, encounters the Ruum which notes that Jim weight 149 lbs. Chase ensues. The chase causes him to lose 10 lbs so he's now outside the 'capture limits'.
Interestingly, I found another (even shorter) synopsis (actually a comparison of 'The Ruum' with 'The Zoo') and it says 'Jim who has been ordered to go back and get the H-9 Ruum they left behind on the third planet'.
Looks like the story itself is quite short and I'm still trying to find a copy of the text. Would like to verify (or refute) that tidbit I found in the Ruum vs Zoo comparison.