The Reds are currently seventh in the Premier League table with 57 points, seven points behind fourth-placed Arsenal, and crashed out of the Champions League at Bayern Munich on Wednesday night.
With five matches of the season remaining it is unlikely that Moyes’ troops will qualify for next season's tournament, and Bosnich believes the Old Trafford side will need to make up for their lack of European football by spending big.
"Manchester United will probably have to spend a little more than £200m," the Australian, who played 33 times for the Old Trafford side over two spells, told talkSPORT. "Money wise, they can afford to be out of the Champions League for a few years. Where they can't afford to fall behind is in their ability to entice top players to the club.
"If you're going to get the best players in the world to play for you, then some of them will take a little less [money] if they know they're going to play in the Champions League. It's the biggest level of football bar none, including the World Cup. That's where it's going to cost them.
"To entice those players you're probably going to have to pay them a little more just because you're not in the Champions League. You have to say, 'I know we're not there this year, but if you come here then you can help us be in it the year after.'"
