Portugal winger Nani believes England could struggle to negotiate the group stage of Euro 2012 without Wayne Rooney.
Rooney is suspended for England's opening two games of the tournament against France and Sweden due to his red card in a qualification game against Montenegro.
He is set to be replaced by either Danny Welbeck or Andy Carroll, but his Manchester United team-mate Nani thinks that could represent a major problem for Roy Hodgson's men.
The 25-year-old told The Sun: "Rooney is a key man and two matches without my United companion could be too much for England.
"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."
He added of the injury blows that have rocked Hodgson's squad: "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."
Nani has his own problems in Group B as Portugal must find a way past pre-tournament favourites Germany and World Cup runners-up Holland.
But he believes his country is better placed than England to enjoy success this summer.
Nani added: "England's opening game against France is very dangerous.
"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.
"People consider Spain, Germany and Holland as the big candidates for the European Championships but Portugal can spring a surprise.
"If we can gain confidence from one match to the next, we can go a long way."