The phrase "expert practitioner" is used to describe someone who has a high level of knowledge and skill in a particular field, but there are many synonyms that can be used instead. Some alternatives include "master", "specialist", "veteran", "proficient", "adept", "skilled", or "experienced". Depending on the context, other possible synonyms might include "guru", "maestro", "savant", "wizard", "ace", or "virtuoso". Each of these terms carries its own connotations and nuances that may be more or less appropriate depending on the situation. Ultimately, the choice of synonym will depend on the tone, context, and intended meaning of the writer or speaker.