King scored in England’s 3-1 friendly win over Mexico on Monday.
He said: “I wouldn’t say it was one of my best games but it was tough out there. They are a good side.
“They move the ball quickly, they’ve got good movement and the manager made it known at half-time that we weren’t getting tight enough. We came out in the second half and did a lot better.”
King has been struggling with chronic knee injuries throughout his career.
“As regards my fitness, the knee is okay, the more I play the fitter I get. I’ve ended the season with three games in 10 days and we’ve got a great set-up here,” he said.
“The medical staff are doing a brilliant job to help me prepare for the games. I’ll try and be as fit as I can and we’ll see where it goes.”
