Rooney scored 19 goals over the campaign but was unable to prevent United slumping to seventh in the table - the club's worst finish since the Premier League began.
Keane, who won seven league titles at Old Trafford, believes Rooney can use the disappointing domestic season as motivation to produce his best in Brazil.
"He's not going into the World Cup on the back of a top season at United in terms of winning trophies, and you could say that for a lot of the England players," Keane said at the launch of ITV's World Cup coverage.
"I think Wayne has had a decent enough season himself, though, and it might actually help him.
"He might use that frustration he has had at United this year to the benefit of England."
Rooney was named in UEFA's team of the tournament after Euro 2004, where he scored four goals, but since then the striker has struggled to produce on the biggest international stage.
In 2006, a foot injury meant Rooney was rushed back for the World Cup in Germany and he was then sent off as England lost in the quarter-finals to Portugal.
He failed to score at the 2010 World Cup and was suspended for the opening two group matches at Euro 2012 after earning a needless red card during qualification.
"There has been that expectation of Wayne going into big tournaments and it has not happened, for one reason or another - but it is certainly not for lack of effort," Keane said.
"Injuries, off the field stuff..
in South Africa 2010 there was allegedly a lot of unrest in the camp."
The Irishman continued: "He has not peaked at the right times at big tournaments.
"A couple of times he's gone into them on the back of injuries, there have been issues off the field.
"England need Wayne to have a decent World Cup, like you need any attacking player in the big teams."
Roy Hodgson has selected the youngest England squad for a World Cup since 1966.
Rooney is only 28 but, with 89 caps to his name, the United frontman is the third most experienced squad member behind Steven Gerrard and Frank Lampard.
Keane says squad harmony will be crucial to how England's best players perform, and reckons the youngsters can inject enthusiasm into the group.
"Roy Hodgson's skills are going to be tested in that way, having a happy group," Keane said.
"That is why I think he has left out one or two senior players who might not be in the starting XI.
"He's gone for younger players who might bring a different type of energy, and, if they are left out, they won't bring any kind of negativity.
"Roy has the experience to manage all that
They look like a decent group and there is a good balance."
Source : PA
Source: PA