Walton has played in midfield for most of the season but played in a unfamiliar right-back position for the games with Wolves and Sheffield United.
The 17-year-old had a nightmare against the Blades and was back playing in the reserves this week against Birmingham and Everton.
Blackwell said in the Yorkshire Evening Post: "Simon had a tough game after doing okay against Wolves. He didn't play well against Sheffield United and I made the decision to take him out for his own good. He's had a tremendous season and he is my young player of the year by a mile. Simon's got a massive future at this club and I'm glad I'm now able to give him a rest."