Jose Mourinho wants a £3m ($3.9m) pay rise on his current £12m-per-year contract at Manchester United after guiding the club to the EFL Cup and the Europa League last season, according to reports.
The Sunday Mirror claims Mourinho, 54, is frustrated that he has not been offered a new contract by the Red Devils despite winning three trophies last season.
The former Chelsea and Inter Milan boss signed a three-year deal to replace Dutchman Louis van Gaal as United boss in the summer of 2016.
His United team have started the 2017/18 season in bright fashion, sitting second in the Premier League table behind Manchester City and nearly through to the round of 16 in the Champions League.
Mourinho raised eyebrows last month when he heaped praise on French club Paris Saint-Germain during an interview and said he would not end his career at Old Trafford.
Mourinho's tactics have come in for criticism from fans and pundits alike since he set up his team conservatively in a dour goalless draw with Liverpool at Anfield on 14 October.
He took another swipe at fans in his programme notes ahead of the Champions League win over Benfica, saying: "I hope you enjoy the game more than some of you did against Tottenham".
But speaking before United's trip to Chelsea on 5 November, Mourinho downplayed reports that he could leave United in the near future and insisted that he was happy at Old Trafford.
"I am happy here – and I love my players," he was reported as saying. "You try to create a story because of my words after defeat at Huddersfield – but there is no story.
"It has just been a difficult week. Big matches, injuries, tiredness... but that is just normal."