Manchester United defender Luke Shaw will miss tomorrow night's (21 September) EFL Cup third-round tie against League One outfit Northampton Town. The left-back underwent a scan after sustaining an injury setback on Sunday as Jose Mourinho's side, who won all of their first four games of the season including the Community Shield victory over Leicester City at Wembley, followed successive defeats to Manchester City and Feyenoord with a shock 3-1 loss at Watford.

Shaw's groin problem is said to be a recurring issue and, according to the Press Association, his scan results revealed a slight tear that will rule him out of the upcoming trip to Sixfields Stadium. The BBC further reports that the 21-year-old, who missed 10 months with a horrific double leg fracture before returning to pre-season action in July, is rated as 50-50 ahead of United's Premier League clash with defending champions Leicester City at Old Trafford at the weekend.

Mourinho substituted Shaw towards the end of a first defeat to Watford in 30 years, evidently riled by the England international's failure to close down winger Nordin Amrabat in the build-up to Juan Camilo Zuniga's late goal just two minutes earlier.

The two men appeared to become embroiled in a stern exchange of views on the bench at Vicarage Road and Mourinho shocked many by singling out Shaw for criticism in a post-match interview.

"The first Man City goal and this second goal against Watford – you can find an incredible similarity, which is [Aleksandar] Kolarov has the ball in a difficult situation in the corner and my players, instead of going up to press they decide to give space," he said.

On Shaw, he added: "And here for the second goal, Amrabat receives the ball and our left-back is 25 metres from him instead of five metres. But even at 25 metres, you have to jump and go and press, but no, we wait. This is a tactical but also a mental attitude. It's something that doesn't become perfect in a couple of weeks."

The Times have subsequently reported that Shaw was attempting to work through the pain barrier at Watford and is unhappy at receiving such public criticism from his manager. They also suggest that many of his teammates are shocked by the treatment of a player with an unfortunate injury history who has also previously seen a sports psychologist since his £27m ($35m) switch from Southampton in 2014.

In terms of United's other fitness concerns ahead of Northampton, Anthony Martial will need to be assessed after being substituted in the first half against Watford following a painful clash of heads with Daryl Janmaat. The French forward played on for a short time and lost out to Miguel Britos before Etienne Capoue netted a controversial opening goal. Henrikh Mkhitaryan has missed the last two games with a thigh injury suffered on international duty with Armenia and Phil Jones is out with a knee problem.