The duo's return is a major setback for Sri Lanka, who suffered a crushing 226-run defeat in the first of the three-test series at Port of Spain on Sunday.
Former captain Mathews, who scored 11 and 31 in the opening test, was determined to make a mark after missing five months of action with hamstring and calf injuries.
Sri Lanka Cricket confirmed Gamage fractured his finger while batting in the first test.
Batsman Dasun Shanaka, who last played a test against Bangladesh in February, and all-rounder Danushka Gunathilaka will be flown out as replacements later on Wednesday evening.
It is unlikely that the duo will be available for the start of the second test at St Lucia on Thursday, given the lengthy flights.
The visitors, though, have Dhananjaya de Silva and Mahela Udawatte as cover for Mathews, and extra quicks Kasun Rajitha and Asitha Fernando to replace Gamage.
First Published: June 13, 2018, 2:18 PM IST