Keane, who is now the assistant manager of the Republic of Ireland, has called for United's experienced stars to coax the younger players out of their slump.
The Mirror quotes him as saying: "Giggsy, Rio, they've got to step up to the plate. One or two of the new players are getting a little bit criticism, but it's up to the players who have been there a few years, who know what Manchester United are about.
"They are lacking a few leaders at the moment. I don't think they have that type of player in the group anyway. There is no point expecting certain players to lead when they are not that type of character.
"There's no problem losing football matches, but you can lose in a good way. The way United have lost the last few games has been more upsetting than anything else. They have to get certain players in, certain characters to make sure they battle for every minute of every game."
United were beaten 3-0 by fierce local rivals Manchester City on Tuesday.