Hargreaves says England need Rooney, no matter their results in the previous two group games.
He told the Daily Mail: "He's older and more experienced now and I'm sure he'll have a positive impact on the team - he won't want to leave the competition early after just getting started. He'll draw on positive experiences.
"He's had pressure on a day-to-day basis since he was a kid. It's not going to be a problem. He's going to come in and give a massive boost to the team and make it a better one. He's the best player England have alongside Steven Gerrard.
"We need him in the team if we want to make it further."