The Red Devils were strongly linked with the Bayern Munich player earlier this summer, but the speculation has since cooled and United have also added Ander Herrera, who plays in a similar position to Kroos.
However, Scholes believes that the "brilliant" 24-year-old would have been one of the best additions that United could have made.
"I love watching Toni Kroos. I think he's brilliant. I love the way he controls the ball and controls games. He can really play a pass and has superb vision. Kroos is capable of scoring goals too, from outside the box on either foot," Scholes wrote in his Paddy Power blog.
"I just wish Man United had signed him. Yes, it is good to see United bringing in new players, but they haven't signed anything like the quality of Kroos."
Kroos is expected to be in the Germany starting lineup for this evening's World Cup clash against Algeria.