Solskjaer out for three months with knee injury
The 30-year-old Norwegian was due to link up with the club on their three-match, 10-day American tour.
Instead he has remained behind to have further treatment following a knee operation that kept him out for most of last season.
Speaking ahead of a training session at the NovaCare Complex, manager Alex Ferguson revealed the extent of Solskjaer's injury.
"When Ole went to get treatment at the end of the season he saw a Swedish specialist, who is reputedly the best in the world," said the Old Trafford boss.
"There was a proviso from the specialist there would possibly be a second step.
"That's the second step we are taking now. It is not a shock, only a disappointment," said Ferguson.
"There were no guarantees (after the operation). It was a trial and hopefully there would be success.
"But we feel now that it has not been 100% successful and that he should take the second phase and go back and see him again.
"It may mean he will be out for five-six weeks. But if it is worse than maybe two or three months."
United trained in high humidity with the temperature in the 80s at the home of the Philadelphia Eagles.
Ferguson is hoping the intense pre-season programme, beginning in America, will kick-start their campaign for the second year running.
United open their Champions World Series on Sunday when they face Bayern Munich in Chicago.
Ferguson, who is aiming to retake the high ground from Arsenal and Chelsea, said: "In years gone we took the easy route of smaller low-scale games that brought our fitness on gradually.
"But last year the competition of the games in America and the intensity of the matches brought an edge to our game which I thought was fantastic.
"It was something new for us and something that made me think a little bit differently.
"That's why I felt coming back to the United States was an important factor in our preparations."
Ferguson also admitted he may be tempted to try and draft in another left back as Gabriel Heinze has been called up by Argentina for the Olympics.
It means the stg£6.9million recruit's debut will be delayed until September - at least.
Ferguson is livid that both Heinze and Portugal's Cristiano Ronaldo are heading for Athens.
And the consequences for the Argentinian could be serious.
"The one thing very apparent in this situation is that here's a lad who may be denied an opportunity to get a career at Manchester United," said Ferguson.
"When I start the season I may have another left back because of this and he may never get a game. He may find it difficult to get in the team.
"At least Ronaldo has proved himself as a Manchester United player so we know where we stand with him.
"For Heinze the opportunity to start his career with us has now been taken away from him."
Ferguson is contemplating giving Ronaldo two months' rest after the Olympics as he also played in Euro 2004.
"We might not use him until November, which is absolutely ridiculous," said the United boss.
"It is a natural thing to want to play for your country but I don't think the two players' careers are being considered here."
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