The US-based player, who rose to No 14 in the world rankings on Monday after reaching the final of the ATP 500 tournament at Queen’s Club at the weekend, last represented the country in the global team competition in September 2011.
The national squad will face Ireland in a Euro-Africa Group II relegation playoff in Centurion, starting on July 17.
“We have until 10 days before the tie to name our team to play Ireland, according to Davis Cup rules,” TSA president and acting chief executive Gavin Crookes said in a statement.
“We are doing all we can to secure a sponsor for Kevin to secure him as part of the team.”
The federation confirmed it was unable to cover the costs required by the big-serving player.