Nani believes Manchester United team-mate Wayne Rooney’s two-match suspension will hinder England significantly at Euro 2012.
Roy Hodgson will have Andy Carroll, Jermain Defoe, Danny Welbeck and Ashley Young to choose from up front for England’s first two games in Group D, against France and Sweden.
Nani, 25, said he hopes England reach the knockout stage, but believes Rooney’s initial absence will harm their chances.
The striker will return to availability for England’s final group match against tournament co-hosts Ukraine.
“Rooney is a key man and two matches without my United companion could be too much for England,” he told The Sun.
“Roo is angry about his absence because he knows he’s the man to score goals and he won’t be there working for the team.
“I sincerely want England to reach the quarter-finals but it’s not going to be easy.”
England have suffered several injuries since Hodgson named his 23-man squad, with Frank Lampard, Gary Cahill and Gareth Barry all having to pull out in the last two weeks.
Nani said: “For an England team without Rooney, Rio Ferdinand, Frank Lampard and Gareth Barry is vulnerable because they are suffering in all departments of the team.
“These players are so important for the team and their replacements are not at the same level.
“These absences place many doubts about the English for the Euros. England need to make their biggest effort because injuries are destroying the team.”
The Portugal livewire believes the winner of England’s match against France will likely go on to top Group D.
“England’s opening game against France is very dangerous,” he said.
“The two teams both need a victory because the result will put a very decisive stamp on the group.
“The losers will receive much criticism and that will generate a lot of pressure for the following game.”