Thankfully for United, Lukaku is expected to return to training on Tuesday after recovering from his ankle problem and this has provided a timely boost ahead of their FA Cup final against Chelsea next weekend.
Mourinho has decided against appointing a direct replacement, so he will lean on his coaches Silvino Louro, Ricardo Formosinho, Carlos Lalín, Emilio Alvarez, and Michael Carrick - who will join the backroom staff next season - for advice instead.
Mourinho has said Carrick will definitely start Sunday's game at home to Watford before he takes him off so the 34-times capped former West Ham and Tottenham Hotspur star can take the accolades from the fans. "It's his knee", the manager said.
The France global has been linked with a move away from the club, with Juventus, Chelsea and Tottenham mooted as possible destinations. "He was injured in the Friday training session and yesterday [Saturday] he couldn't train".
"The moment he's my assistant he will help in every aspect".
Faria has followed Mourinho around as his No.2 for the last 17 years - joining him at Porto, Chelsea, Real Madrid and Inter Milan.
Mourinho added: "I will miss my friend and that is the hardest thing for me, but his happiness is more important and, of course, I respect his decision, especially because I know that we will always be together".
"I don't think it makes sense when Rui is leaving after 17 years".
"I'm going to have coaches, assistant coaches, I'm going to have fitness coaches and a structure where they have specialists in different areas".
"We spend more time with each other than anybody else in our lives. [Faria] is the one who is the closest to a brother".
"I would like to thank him for the opportunity and confidence, for the knowledge and experience, but most importantly for his friendship. I'm sure he'll try to improve the level of the squad".
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