The former Arsenal boss believes it will be difficult to secure top players in a highly competitive market.
The Red Devils dropped two points against Chelsea on Sunday, having taken the lead through Juan Mata’s strike, after David de Gea spilled Antonio Rudiger’s shot to allow Marcos Alonso to equalise.
United are now without a win in their last four games and are expected to make a number of signings this summer transfer window as Solskjaer looks to put his own mark on the team.
But Wenger has warned it will be difficult to secure new names, telling beIN Sports: “They spent a lot of money. They still have a lot of money, but they have a big job to do.
“What will be interesting in the summer for me is that you have many big clubs who will be out to buy players and I think there will be more money than good players on the market so it will not be easy to get it right.
“Because you will have Real Madrid out there, you will have Bayern Munich, Paris Saint-Germain, Man Utd, Arsenal and Chelsea out there on the market, so there is more money than good players. And that will be the big problem for all the big clubs.”
United are still yet to win a Premier League title since the departure of Sir Alex Ferguson in 2013, and Solskjaer is the fourth permanent manager at the club since the Scot retired.
Asked why the Red Devils have struggled so much, Wenger said: “I would say it was three main factors. First of all, Alex Ferguson was a huge personality in the game. His importance at the club and his quality, of course, was dominant.
“After that, I believe when he stopped it was also the end of a generation, coinciding with Ryan Giggs retiring. Exceptional players who came to an end.
“And the other thing is the recruitment policy was not successful, and the older generation was the spirit of Man Utd.
So they lost the quality and the spirit because all these players were willing to die for Man Utd, plus the players they bought have not all been successful. And these three things together show that it’s not easy to keep continued success.”