The England number one's season has been littered with high-profile errors, with the latest coming in injury time against the Hammers when he allowed Andy Carroll's shot to go through his hands and legs.
The late strike had no effect on the result, but Platt has insisted that a back spasm the goalkeeper suffered earlier in the game was a factor in the goal conceded.
"I think his back spasmed as he kicked the ball," said Platt. "He is a bit blocked up in there and will be sore in the morning.
"It was probably a contributory factor in the goal, clearly. If he is carrying that kind of injury then he can't get down there. His back just spasmed and he couldn't get down low to the ball.
"Most keepers, because they are throwing themselves around all day during the week, have an issue like that, but it's a 24-hour thing, really."
Manchester City sit in second place in the Premier League behind newly-crowned champions Manchester United.