In an exclusive interview with the official club channel, Moyes revealed that the striker reported the injury on the day the Reds flew out to Bangkok, and after further investigations into the problem on arrival in Thailand's capital it was agreed that the best way forward to treat Rooney would be for him to return to the Aon Training Complex in Manchester.
"It's disappointing," Moyes told MUTV. "The day we left [Manchester for the tour] he just felt his hamstring tighten up right at the end of training and we thought there would be no problem. 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 and we thought it would be worth just seeing what it was and there was a very slight mark on his hamstring. We won't take any chances - there is no point in taking him any further round the world so we've sent him back and he'll get treatment at the Aon Training Complex."