Injured Rooney leaves United tour
Rooney suffered the injury in training on Thursday and scans have revealed the full extent of the damage.
"Following a scan this evening on a hamstring injury sustained in training, it has been decided Wayne Rooney should return home immediately for further assessment and rehabilitation," the club said in a statement.
The news is an unexpected development given United only landed in Bangkok on Thursday morning and went straight to their hotel for a short rest ahead of what turned out to be Rooney's single training session.
Sixteen hours later he is on his way to the airport to begin the marathon journey back to Manchester.
If Rooney is ruled out for a month it would mean he could be struggling to be fit for the Community Shield against Wigan at Wembley on August 11.
And given his obvious lack of match practice, it is difficult to see how he could be involved in the following week's clash between England and Scotland, or start the Premier League opener at Swansea on August 17.
The incident comes just a day after manager David Moyes revealed United staff had told him Rooney had returned for pre-season training in his best shape for years.
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