(CNN) -- England international striker Wayne Rooney is struggling to make the start of Manchester United's Premier League title defense after picking up a stomach virus on his club's preseason tour of Nigeria.
Rooney is almost certain to miss the opening Premier League game against Newcastle.
United manager Alex Ferguson revealed the problem at a news conference on Tuesday, saying that Rooney would miss this weekend's traditional Community Shield season-opener against FA Cup winners Portsmouth at Wembley.
The two teams also faced each other in Nigeria last week, a match United won 2-1, but Rooney has barely trained since after going down with the illness.
Ferguson told Sky Sports News: "I doubt we'll get Rooney fit for the start of the season with the virus he's had.
"It's a virus he picked up in Nigeria and it's not a nice one, but quite a few have had it," said the Scot, who confirmed that Rooney was not suffering from malaria.
His absence is a serious blow for the European and Premier League champions who are already missing Cristiano Ronaldo, who had an operation on his ankle after playing for Portugal in Euro 2008.
But there was good news for United fans as Ferguson insisted again that there was no chance of Ronaldo being allowed to join Real Madrid.
"The matter is now closed. Trust me he will play here next season," Ferguson said.
With currently sidelined Louis Saha also set to leave Old Trafford, Ferguson is down to Carlos Tevez and youngster Frazier Campbell as recognized strikers ahead of their first league match against Newcastle on August 17.
The unwelcome development may lead United to step up their pursuit of Tottenham's Bulgarian international striker Dimitar Berbatov, who has been consistently linked with a move to Old Trafford.
Another Manchester United player who will be missing from the squad to face Portsmouth and the season's start will be Brazilian Anderson.
The 20-year-old midfielder is on international duty at the Olympics in Beijing and will not return to the club until mid-August at the earliest.
Rooney's illness means he could also miss England's friendly against the Czech Republic on August 20 at Wembley as Fabio Capello's men build up to important World Cup qualifying games in the autumn.
There is also a big doubt about Liverpool skipper Steven Gerrard who limped off after 27 minutes of Tuesday's 4-1 win over Valerenga in Norway.
The midfielder appeared to suffer a thigh strain and the Reds will hope they took Gerrard out of the action before any serious damage could be done.
But with a Champions League qualifier in a week's time against Standard Liege, it is a problem boss Rafael Benitez could do without.
Benitez also saw players he may have to sell soon -- Xabi Alonso and Yossi Benayoun -- score outstanding goals.
Both could be used to raise the cash to buy Gareth Barry from Aston Villa. Roma have admitted an interest in Benayoun while Arsenal are being linked with Alonso.
Alonso stole the show with a 20th-minute strike from 25 yards following Robbie Keane's flick on. Fernando Torres and French striker Ngog were also on target.
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