Manchester United slipped to a second defeat from their last four Premier League matches with Matt Ritchie firing Newcastle to a huge three points.
The Red Devils are currently stuck in a rut with several of their best players coming in for criticism.
Pogba produced a turgid display against Newcastle with Alexis Sanchez, Romelu Lukaku and Anthony Martial all struggling to show their best form.
And the Manchester Evening News say Manchester United players think Mourinho is worried about the performances of Pogba and Matic in the middle of the park.
Both players started the season in fine fettle.
Pogba appeared liberated in the early weeks of the campaign, scoring big goals in wins against West Ham and Swansea.
Many believed Matic’s arrival from Chelsea was the reason why Pogba has impressed, with the Serbia international signed to give his new team-mate the freedom to roam.
But the MEN say a number of United players have noticed concerns by Mourinho over Pogba and Matic in recent weeks.
It is said things got heated during the club’s recent 2-0 win over Huddersfield, where Pogba was left on the bench.
The 24-year-old’s struggles are currently well-documented.
Pundits such as Graeme Souness, Gary Neville and Martin Keown have been quick to accuse the France international of being tactically naive and lacking footballing intelligence.
But Matic’s plight has gone under the radar.
The Serbia international looks in sore need of a rest having been carrying an injury in recent times.
Still, however, Mourinho has persevered with the two-time Premier League champion despite the impressive form of youngster Scott McTominay.
Both midfielders will need to up their game amid reports United will sign a midfielder when the transfer window reopens in the summer.
Bayern Munich’s Arturo Vidal has reportedly been earmarked as a priority target.
But Borussia Dortmund’s Julian Weigl and Napoli’s Jorginho are also on their list.