For an initial assessment, keep the complete player contract and amendments, the medical confirmation to the extent needed, the injury notice, examinations, club instructions, pay statements and payment records. For variable pay, add appearance data, bonus rules and the season schedule.
Create a timeline with the injury event, first notice, start of incapacity, treatment, checks, attempted return, pay statement and payment. Mark which document supports each entry. This shows whether the dispute concerns the cause, period, treatment, cooperation or calculation.
Limit health data to what the legal review requires. A certificate covering incapacity may be enough for the first assessment. Detailed findings should go only to people who need them for treatment or a specific legal review.