United have signed just three players so far this summer, including Ander Herrera from Athletic Bilbao for £29m.
With just over two weeks remaining in the transfer window, Scholes believes that manager Louis van Gaal is in need of boosting his squad further.
The 39-year-old told BT Sport: "He hasn't really strengthened his squad probably as he would have liked. I think he's crying out for midfield players, he's probably crying out for defenders, but not just any old midfield players, it has to be the right quality of player to play at this club and make the squad better."
United start the new Premier League season later today when they face Swansea City at Old Trafford.