The Red Devils stunned tournament top favourites Brazil 2-1 in the quarterfinals at the Kazan Arena on Friday.
"Belgium is the country that has impressed me most so far at the World Cup," Gyan told Hot FM.
Gyan, however, declined to predict the ultimate winner of the tournament, with Belgium one game away from the final.
"To be honest, I can't predict who will win the tournament because it's too tricky. There have been several shocks and it will continue until the tournament is over.
"It's too tricky to predict so I will only say that the best and well composed country will win at the end of the tournament. Belgium have a good team and teamwork but it's still too difficult for me to say that they will be the eventual winners," he added.