From what I've heard. The "injury" was re-injured during sparring 3 weeks before the fight. Pac and a sparring partner bumped shoulders as Pac came in. They threw out the media ever since then, saying they wanted to keep their game plan a secret. One of Pacquiao sparring partner Dashon Johnson said this on his facebook. Pacquiao says Mayweather was leaked shoulder injury news - Business Insider He was sent home because Pac's shoulder injury prevented Pac from sparring and the injury was to be kept a secret. But Mayweathers camp found out about it. Leonard Ellerbe even said he knew everything going on in Pacquiaos camp and said Pacquiao was having a rough camp. More links Sparring partner says Pacquiao’s shoulder was “messed up pretty bad” and Boxing News 2015: Sparring Partner Confirms Manny Pacquiao Injured Shoulder in Training Camp : Sports : Latin Post These articles are all over the place.

They thought Pacquiao would be fine and fight through it on fight night as long as they had the pain killer they asked for. Either it was Floyd's elusiveness that caused Pacquiao to only throw 400 punches or it was the injury.