David Moyes has revealed that Wayne Rooney complained about a tightening in his hamstring before Manchester United flew to Bangkok on Wednesday for the start of their pre-season tour.
Rooney had to return home after only one day of United's trip to the Far East with the injury, a grade one tear of the joint, describing himself as "gutted" at having to miss out on the chance to play for the champions under their new manager during a three-week trip that also includes stops in Sydney, Japan and Hong Kong.
Speaking to MUTV, Moyes said: "It's disappointing. The day we left [Manchester] 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 [Thursday] 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."
United believe Rooney, who had been described by Moyes as being in his best physical shape for many years, will be unavailable for at least a month, raising questions about the club's decision to fly the player 6,000 miles to Thailand knowing that doing so could put his physical conditioning at risk.
Writing on Facebook shortly after his injury was confirmed, Rooney said: "Gutted to have picked up a niggling injury especially as training was going so well, heading back to Manchester to have it assessed fully but early indications are nothing to worry about."
There was already doubt that, with Rooney unsettled at United and refusing to confirm he wants to stay, the forward would start the campaign in United colours. The hamstring injury further clouds the future of the striker, who was pictured at Glastonbury the weekend before he reported back to United for pre-season training.
In a statement on Thursday, United said: "Following a scan this evening on a hamstring injury sustained in training, it has been decided that Wayne Rooney should return home immediately for further assessment and rehabilitation. It is anticipated he will be unavailable for selection for a month."
Moyes has reiterated that Rooney is not for sale, but the sense remains that if the club received a serious bid, in the region of £30m, they would consider letting the 27-year-old leave.
Now it remains to be seen whether he will decide to make it clear he views his long-term future at United. Before his injury, Rooney had appeared in good spirits, being photographed smiling alongside Patrice Evra, as Moyes prepared for Saturday's game with a Singha All Star XI.
United play Wigan in the Community Shield on 11 August and start their Premier League season the following weekend. Rooney must be a major doubt for England's friendly against Scotland on 14 August.