Romelu Lukaku insists Jose Mourinho is "really cool" behind the scenes and his demeanour in public is down to a winning mentality.
Mourinho's critics believe the Manchester United manager has been negative during pre-season regarding transfers and the late finishing of the World Cup, but Lukaku has sprung to his defence.
Speaking to Business Insider, the United striker says he sees a different side to Mourinho, and is close to the manager.
"I get to see a total different image of him where he's really cool," Lukaku said. "People need to understand that we play this game not to lose it. We play this game to win.
"So when you lose, you get angry, you get upset. So for him... when he's upset, he's a type of person that you can really see that he's mad or angry. So I think this is normal."
Lukaku, who was signed by Mourinho from Everton last summer, scored 27 goals in 51 games in his debut season at Old Trafford.
The 25-year-old revealed Mourinho would even send him funny videos or advice, and insists he likes playing under the Portuguese boss.
"We make jokes. He would send me like sometimes good advice, or funny videos, some stuff like that. So he's really a family guy. That's how I know him," he said.
"We have a good relationship. I think it's nice to play for him."