Manchester United fear Luke Shaw could be out for at least a month with a hamstring injury, sources have told ESPN FC.

The left-back was forced off in the first half of the 2-1 defeat to Crystal Palace on Saturday after suffering a right hamstring strain.

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The 24-year-old is set to miss the trip to former club Southampton on Saturday, United's last game before the international break.

He is unlikely to make Gareth Southgate's England squad for games against Bulgaria and Kosovo and could also miss Leicester's visit to Old Trafford on Sept. 14.

Shaw is set to undergo more tests this week, but there is concern he could be sidelined for closer to six weeks, ruling him out of the home game against Arsenal on Sept. 30.

Ashley Young is in line to start his first game of the season against Southampton after the 34-year-old replaced Shaw against Palace. Marcos Rojo, who is wanted by Marseille, AC Milan and Monaco, could also step in.

However, manager Ole Gunnar Solskjaer will not be able to call on Diogo Dalot.

The 20-year-old can play in both full-back positions but has been ruled out until after the international break after picking up an injury in training.

United are looking to get back on track at St. Mary's on Saturday lunchtime after a miserable defeat to Palace.

Solskjaer's team have four points from their opening two games after victory over Chelsea and a draw with Wolves.

Meanwhile, sources have told ESPN FC that Brazilian midfielder Fred will not leave the club before the European transfer deadline on Sep. 2.

He has been linked with a move to Fiorentina, but the 26-year-old is in Solskjaer's plans despite not featuring in the opening three games of the season.