Sri Lanka's first rivals Namibia are returning to World Cup stage after competing in the 2003 edition.
Wicket-Keeper batsman, Perera suffered a right shoulder sprain during training, Sri Lanka Cricket said in a statement.
Sri Lanka will play three T20Is -- on June 23, 24 and 26 --, which will be followed by three One-day Internationals on June 29, July 1 and 4.
New Sri Lanka captain Kusal Perera said he wants to build a culture in which players have confidence.
Ater losing the opening game against Sri Lanka, Indian skipper Rohit Sharma said players will learn from their mistakes.