In an ideal world, each new joiner is expected to be trained with the practices and standards applied on the project. Happens that the ideal world is far from reality. When project starts getting off track, is not rare to have more manpower added on it, which is doomed to failure.
Right now, the project is lacking people and a new developer has joined the team. His programming background is known for his low quality. On his first experiences on the team, he demonstrated a lack of a clarity on what he was doing, and if he keeps work like this he'll increase the project's technical debt.
Right now, the first mitigation - which is already proven valid - is the implementation of code review. However, it takes time and dedication from both people involved, which would impact the project plan.
How should this situation be dealt with?