The jockey will be out of the saddle for six weeks after fracturing his kneecap when falling from a horse.
Campbell said he the incident seemed innocuous at the time.
"It was just he way I hit the ground.
"I was just exercising a horse and it bucked me off the side and I landed funny.
"I have had way worse falls than that. It was just an awkward landing.
"I got back on it afterwards an then rode another one, but then the pain got worse and worse.Campbell was later diagnosed with a broken kneecap and put in a knee brace.
He will be off work while he recuperates.Campbell said he hoped to be back riding at the races at the Wingatui meeting on March 2.
"It is just one of those things, I suppose. There is not much you can do about it."
Campbell leads the national apprentices premiership despite having had another stint on the sidelines through injury earlier this season.
His 28 wins puts him two ahead of northern apprentice Ryan Elliot.
Campbell is not the only White Robe Lodge rider absent. Shankar Muniandy left North Taieri to continue his riding career in Malaysia at the end of last month.
