Jose Mourinho has claimed Manchester United have not spent enough in the transfer market to match Manchester City, who "buy full-backs for the price of strikers".
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.
The result means City can move 15 points clear at the top of the table if they beat Newcastle United on Wednesday and leaves Mourinho's side facing what looks to be an impossible task in the Premier League title race.
Pep Guardiola's side have been in irresistible form this term following an investment of close to £225million in the last transfer window, which included the arrival of full-backs Kyle Walker and Benjamin Mendy in big-money deals. England international Walker left Tottenham in a deal worth in the region of £45m, while Mendy, who joined from Monaco, cost close to £52m, making him the club's third most expensive transfer in history behind Raheem Sterling and Kevin De Bruyne.
City forked out roughly £191m in Guardiola's first year in charge, but United's spending under Mourinho has not been much below that of their neighbours, with close to £300m spent since he took over in May last year.
However, Mourinho feels United must still spend more to match City and are being "punished" in the market because of their illustrious history.
"When you say a club like Manchester United, do you think [AC] Milan is not as big as us?" he told a news conference. "You think they are not as big as we are?
"Do you think Real Madrid are not as big as we are? You think Inter is not as big as we are? There are many big clubs and you say big clubs, I know what is a big club.
"One thing is a big club and another thing is a big football team that you know is not one of the best teams in the world, so when you speak about responsibilities to win the Premier League, Tottenham does not have that responsibility. Tottenham is not a club with the same history as us. Arsenal doesn't have the responsibility to win it, Chelsea doesn't have the responsibility to win it.
"Manchester City buy full-backs for the price of the strikers, so when you speak about big football clubs, you are speaking about the history of the club."
When reminded about his spending at United, he replied: "It's not enough, it's not enough. And the price for the big clubs is different from the other clubs, so the big, historical clubs are normally punished in the market for that history."
Mourinho's comments came after a draw that means his side have taken only eight points from a possible 15 in their most recent Premier League fixtures.
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.
"The boys are doing what they can and they are doing fine," he said. "I say, last two matches, we had 15 chances to score and we concede three 'S' goals and an amazing free-kick.
"So the boys do what they can, they are trying hard with the problems and injuries we have. I am not happy with the result, and against Leicester, but I am happy with my players."
