Sheringham was part of United's 1999 Treble winning team.
"Rooney will score goals if he is given the right kind of set-up to work in. He has proved that time and again down the years," Sheringham told ESPN.
"All I would say is playing up front on your own is very tough.
"Not many players can pull that off successfully. I certainly wouldn't have fancied trying to play that role and always had a partner alongside me.
"Van Gaal is trying something different at Manchester United and it is not quite suiting Rooney at the moment.
You have a top-quality player there, so you would like to think there is a way of finding a system that will suit him. It is up to the manager to work that out."