Mascherano missed Saturday's 4-0 Premier League rout of Burnley with a pelvic injury sustained on international duty with Argentina.
"He went to South America with a slight problem and played," Liverpool manager Rafa Benitez told reporters on Monday.
"Afterwards he needed to check it out so we decided he should do it over there and miss our game at the weekend. It was not serious, only a minor thing, and he will be fit to play in the Champions League."
"We have to know they are two massive competitions so both are important," said the Spaniard. "If you are asking what is more important, both are more or less at the same level but our fans would like to win the Premier League.
"We would be really pleased if we could do that but I don't think anyone would not want to win the Champions League so we have to approach the competition thinking that it is massive, a big trophy, and we will try to win it from the first day."
