Kevin Mbabu’s facing a spell on the sidelines after suffering an injury at the Etihad Stadium.
The Newcastle United defender felt his hamstring as attempted to stop Sergio Aguero scoring his third goal in Saturday’s 6-1 defeat to Manchester City.
And Mbabu will have a scan in the early part of this week to determine the extent of the problem.
The 20-year-old had started the club’s last two Premier League games at left-back in the absence of injured pair Massadio Haidara and Paul Dummett.
However, both Haidara (knee) and Dummett (hamstring) could be available for the October 18 home game against Norwich City, which follows the international break.
Injuries have already taken a toll at United, where McClaren is without a number of key players just two months into the new campaign.
Steven Taylor is sidelined with a long-term hamstring injury, while Jack Colback, Rolando Aarons, Gabriel Obertan and Karl Darlow are also in the treatment room.
And the return of Haidara and Dummett to fitness is timely for McClaren.
Meanwhile, Mbabu, signed from Swiss club Servette in January 2013, made his debut off the bench in last month’s Capital One Cup tie against Sheffield Wednesday.
He impressed on his league debut Chelsea, and McClaren no had qualms about putting him in against City.
Mbabu had been a candidate for a loan spell at a Football league club before a bout of sickness saw him pitched in against Wednesday.