After United's 1-0 victory over Benfica on Wednesday evening, Mourinho complained about managers who "cry and cry and cry" about injuries, and this was seen as a dig at current Chelsea boss Antonio Conte.
Conte responded to the comments from the Portuguese coach after Chelsea's 3-3 draw with Roma by telling Mourinho to stop worrying about his former club and focus on his own team.
Nicholas sided with Conte and revealed his confusion about Mourinho's comments criticising other managers complaints, when he "cried all last year" at Old Trafford.
The pundit told 'Sky Sports': "I accept (Antonio) Conte's response.
"He (Mourinho) cried all last year and all of last season at Manchester United. He actually got it to a fine art at one stage, he always looked miserable and still looks like he's miserable.
"He likes to take on the world and play this, 'I'm the enemy,' card and he's very talented at it. But where this comes from (I don't know), I mean I hear him moan all the time.
"He signed Zlatan (Ibrahimovic) when he was injured, but he can't stop that he's injured and that's something he doesn't moan about, but why say it?"
Unitd's style of play under Mourinho has also been criticised after last week's dull 0-0 draw against Liverpool, and Nicholas believes Mourinho created the war of words with his counterpart at Chelsea to create a distraction from the criticism.
"It's camouflage, its deflection, it's a spin of some kind. The thing is Manchester United are being asked questions about their style, I don't (ask questions), it's not an Alex Ferguson style this is a Mourinho style and he's brilliant at it," Nicholas added.
"If he'd taken nothing from Anfield, he'd have been absolutely slaughtered, but he got a result and a good result for them and then he wins in Benfica - they didn't play well again.
"What he's doing is saying, 'I'm not moaning about it', but I keep hearing him talking about Fellaini and Pogba.
"They spent a fortune over the summer, making the squad stronger and I think before a ball was kicked this season we all asked, 'who's got the strongest squad?' and I think we all said Manchester United."