City spent more than £50m each this summer on Kyle Walker from Tottenham Hotspur and Benjamin Mendy from Monaco.
Mourinho said that he would need to spend more, because the £300m he has spent at Old Trafford is “not enough”.
United spent £75m on Romelu Lukaku this summer and £89m on Paul Pogba last year, the two biggest signings ever by a British club.
Wenger has spent far less than that over the years and raised an eyebrow at Mourinho’s claim that United have far less resources than City.
“I have been in that position for 21 years so I can’t start to complain now,” said Wenger pointedly.
“There have always been three or four teams richer than I am. I’ve learned to cope with that. We deal with our own situation as well as we can. Manchester City, Chelsea and Manchester United are all richer than us. We have to find ways to be successful.”
The Frenchman also admitted that he expects to be busy during the January transfer window as Arsenal look to strengthen for the second half of the season.
"I will be busy yes because first of all you have clubs who call you to get players on loan or to buy your players, Wenger said.
"I am open-minded on any possibility to strengthen our team."
The Arsenal manager added that there have been no updates on the future of Alexis Sanchez, who looks set to leave in the summer when his current Arsenal contract expires.
He said: "No, honestly, no. We have not been approached and I stick to what I said before." PLACE YOUR TEXT ADVERT BELOW:>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> How I Made Me =N=2.5 MILLION In 7 Days from 2 Common Product I Imported and how you can do the same. Click HERE FOR FREE Details right now Warning To Men: This 3 Foods Is Killing Your Erection. Click Here To Know Them