If he selects Rondon and he performs at the same level we've seen, then the manager has to take full responsibility. There is no one else that can be blamed.
The choice is to blood a young player or stick with the underperforming senior player. At some point you have to roll the dice and give someone a chance. It might well not work, but at least you are trying to build something for down the line. Losing with senior players achieves nothing except creating resentment a feeling that there is no pathway to the first team.