Speaking to official club media, Ole Gunnar Solskjaer said: "Unfortunately, it's worse news on Alex Telles than we hoped for.
"His ankle injury is a little bit more severe than we hoped and he'll be out for a little spell at least, the whole of August I would think.
"It's not great but that is football. We've got kids wanting to play of course. Brandon Williams has done well in the left-back position."
Telles picked up an ankle injury last week in training, forcing him to miss the 4-2 friendly defeat against Queens Park Rangers. However, the issue appears to be quite serious.
Solskjaer will now be hoping that Luke Shaw will recover in time for the start of Manchester United's 2020/21 Premier League campaign season after breaking his ribs at Euro 2020 with England.
