Odd/dumb Question: Have Two Fighters Who Are Due To Fight Sparred Each Other In The Build-up?

Yep.
Leo Santa Cruz vs Jose Cayetano

Cayetano was suppose to be an easy mark for LSC to beat up on in front of a record viewers on the Fight of the Century undercard. He was LSC 's long time sparring partner and they threw im in the fight at the last minute. He was thought than they thought he would be and he went the distance and made LSC struggle.
Cayeto was a career 118 fighter and they brought him up to 126 on short notice and against LSC who he was just training with weeks prior to the fight.

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The way Jose made Leo chase him I knew that Leo could not really box and his only way to win was pressure. Beating up on sparring partners did not prepare that chump for Carl Frampton's superior boxing style.

 

Lots of guys eventually fought their old sparring partners. Mike Tyson fought McCall. Ali fought Holmes, etc. I'm sure in the early days of the sport guys would fight their sparring partners all the time as they traveled from town to town putting on exhibitions.

 

Nitpick, but Tyson never fought McCall did he?