The 21-year-old Barath has failed to recover from a hamstring injury sustained in the first One-Day International last week and will not feature in the two-match series which bowls off Friday here.
However, the West Indies Cricket Board said the right-hander would remain with the squad here to "continue his rehabilitation with physiotherapist CJ Clark".
The injury is another huge setback for the Trinidadian who only returned to action during India's tour of the Caribbean back in June, following another layoff for a similar problem.
He sustained the injury prior to the World Cup and was forced to miss the tournament.
Simmons, meanwhile, will get another chance to prove himself in the game's longer version after being dropped after a string of failures against Pakistan and India this year.
He has experienced a purple patch of form in the three-match ODI series, with scores of 122 and 80 in the two matches. He missed the third game on Tuesday with a sore back.
The first Test is scheduled to run Oct 21-25 at the Zahur Ahmed Chowdhury Stadium here, with the second match carded for Oct 29 to Nov 3 at the Sher-e-Bangla National Cricket Stadium in Dhaka.
Simmons replaces injured Barath against Bangladesh
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