United have lost two of their first four matches at the start of the 2018-19 Premier League season, and Mourinho's long-term future at Old Trafford is far from secure amid a testing period.
The 20-time English champions have been linked with a swoop for former Real Madrid boss Zinedine Zidane amid speculation that Mourinho is in the latter stages of his tenure at United.
However, Sport Bild reports that Nuno is also under consideration, with the Portuguese - who played under Mourinho at Porto and has Jorge Mendes as his agent - impressing since arriving at Wolves.
Nuno led Wolves to the Championship title last season, and the club have also made a positive start to the 2018-19 Premier League campaign, with five points from their first four matches leaving them in 11th position.
United will return to Premier League action away to Watford after the international break.