Needs to show plays for his country i suppose, not sure, olympic rules apparently.
This is an extract from an article published prior to the 2008 Olympics.
The Road to Olympic Tennis
How Players Qualify and Get Chosen for Their Olympic Tennis Teams
By Jeff Cooper, About.com Guide
The two main criteria for making your nation's Olympic tennis team are your ranking on the ATP or WTA tour and a requirement that you have made yourself available to play in the International Team Championships of the International Tennis Federation (ITF) for at least two of the years 2005, 2006, 2007, or 2008, including at least once in 2007 or 2008. Availability to play in one Fed Cup or Davis Cup Tie fulfills the requirement for a given year. You must also be free of any anti-doping sanctions at the time of selection.
Your ranking as of June 9, 2008 [8 weeks before start of Games] determines your eligibility for Direct Acceptance into the singles and doubles draws. The men's and women's singles draws will each have 64 players; the men's and women's doubles, 32 teams. No mixed doubles event will be played.* The maximum number of competitors allowed will be 172, forcing some overlap between singles and doubles competitors.
In addition, each country can only nominate
6 men and 6 women players, with only 4 men and 4 women players being eligible to play
in the men's and women's singles, and the men's/women's doubles.*
Mixed doubles will be played from 2012 onwards. The Rules for the 2012 Olympics are not yet available.