"He's a happy guy, he's working extremely well", the Portuguese tactician reiterated.
"I am very pleased with his attitude overall and then it's easier to play well".
The Red Devils, who won three trophies last season, are now riding high in the Premier League and remain unbeaten so far this season.
Martial is now battling Marcus Rashford for playing time, but he seems to be thriving in the position battle, as he's scored four goals already across all competitions. We go to win every match, but if its impossible to win all the time we try to get points.
Anthony Martial has been backed to become a "force" to be reckoned with by Manchester United team-mate Jesse Lingard.
We should, rather than pitting them against each other, express delight at the unsafe dynamic on the left hand side now at Mourinho's disposal.
Mourinho is confident that something special is growing at Old Trafford and says supporters around the world should be rejoicing.
Double boost for Chelsea ahead of trip to Stoke I'm not interested to continue talking about this issue. 'I'm working with my players and I'm happy to be working with them. The Italian was asked about the breakdown in relations with Costa, but met the question with a firm rebuttal.
The 21-year-old French global has started just one league match for Jose Mourinho this season but came off the bench to score a penalty in last week's 4-0 win over Everton.
"If he plays down the middle, he is bound to score goals", Lingard told MUTV when asked about Rashford.
With Manchester United putting out a reserve team midweek against Burton in the League cup it will be interesting to see if any of those players force their way into Mourhino's starting eleven on Saturday.
United finished sixth in 2016/17 in Mourinho's debut campaign but have been boosted by the summer arrivals of Romelu Lukaku and Nemanja Matic and have won all three of their opening games in comfortable fashion.
"All of them give me options".
"And I see tomorrow as a hard match".
"We look happy playing football at this moment, that's what I like".
"It's a bit of a headache for the manager but it is a good headache for him to have".
United booked their place in the fourth round and after the game, the draw was made live on Sky Sports News where it was revealed they face a trip to Swansea next.