The League Cup holders were knocked out at the quarter-final stage of this year's competition by Sky Bet Championship side Bristol City on Wednesday after Korey Smith's injury-time victor.
United made it three games without a win in all competitions as they drew 2-2 with Burnley on Tuesday, with Jesse Lingard scoring twice in the second half to salvage a point after strikes from Ashley Barnes and Steven Defour before the break.
It was put to Mourinho that while Guardiola has spent £361.1million since arriving at the Etihad Stadium, he has also spent £286.3m since taking over at Old Trafford.
"I don't get United", said ex-England winger Chris Waddle.
'They are trying hard with the problems and injuries we have. You think Inter is not as big as we are?
Never give up. We knew we had another 45 minutes to play so we had to be patient, keep moving the ball, moving Burnley about, and eventually we created two clear-cut chances which we scored from. Tottenham is not a club with the same history as us.
Mourinho said in August that he felt United were candidates to lift their first title since 2013 this season but dismissed suggestions that two wins in six means they are under-performing.
"Manchester City buy full-backs for the price of strikers".
He replied: "It is not enough, is not enough".
'The price for the big clubs, the price for the big clubs is different from the other clubs, ' he added.
The draw is another commendable result for Burnley on the road this season, with Sean Dyche's side having beaten Chelsea and Everton and taken points away at Liverpool and Tottenham Hotspur, but they - just like United - are unlikely to celebrate with much gusto.
But the former Chelsea boss insists he has been happy with the performance of his players on the whole in the stalemates with Leicester City and Burnley in recent days.
"So the boys are doing what they can and they are doing fine". 'You say seven points from 15, I say last two matches we had 15 chances to score and we conceded three "S" [s***] goals and an wonderful free-kick.
United's players looked ashen-faced as they traipsed onto the bus at Leicester, where they were on course for a comeback win after Mata's first top-flight brace since March 2015 cancelled out Jamie Vardy's opener. That led to a long procession of United attacks as they desperately looked for an equaliser although Lukaku hardly covered himself with glory as he mistimed his jump and failed to connect with Marcus Rashford's inviting cross soon after.