The news was confirmed on Barca's official website on Thursday, after the Spain international missed training.
Gastroenteritis is a stomach bug that can cause diarrhoea, vomiting and abdominal pain.
"The first team player Pedro Rodriguez has gastroenteritis and is undergoing antibiotic treatment," a brief club statement read.
"He is doubtful for the game this Sunday against Elche."
Pedro featured in all but one of Barca's La Liga fixtures last season, scoring 15 league goals as the Catalan giants finished second behind Atletico Madrid.