London - Manchester United manager David Moyes said there was no point in risking Wayne Rooney on the team's tour of the Far East, which is why the injured striker was returning home just hours after arriving in Bangkok.
"We won't take any chances, there is no point in taking him any further around the world," Moyes told Manchester United TV (MUTV) from the Thai capital, explaining that Rooney suffered the injury before leaving England.
"The day we left, he just felt his hamstring tighten up right at the end of training and we thought there would be no problem," the Scot added.
"But after the long flight, we decided we'd get him tested and scanned and have a look at things and there is just a small grade one injury there.
"He didn't train yesterday. We won't take any chances - there is no point in taking him any further round the world so we've sent him back (for treatment)."
The 27-year-old faces a month on the sidelines after suffering the injury and is doubtful for the Community Shield against FA Cup winners Wigan Athletic at Wembley on Aug 11 and England's friendly against Scotland three days later.
United begin their Premier League title defence at Swansea City on August 17.
Rooney has been the subject of transfer speculation since retired United manager Alex Ferguson said at the end of last season the England forward had asked to leave the club.
However, Moyes reiterated on Wednesday the striker was not for sale and would not be leaving Old Trafford.
United open their tour against a Singha All-Star XI in Bangkok on Saturday and will also play in Sydney, Yokohama, Osaka and Hong Kong before facing AIK in Stockholm on August 6.
They have left Manchester without captain Nemanja Vidic, who is struggling with sciatica. The club said it was not serious and expected the Serbia centre back to join them at some point.