The colourful batsman was excluded without an explanation by the England Cricket Board earlier this week, but the PM has praised the South Africa-born Pietersen and admitted that KP's friend Piers Morgan made a "powerful argument" to have him recalled.
Speaking to BBC Sport, the Tory leader said: "I am an enormous fan of Kevin Pietersen and I have had some of my most enjoyable times watching him tonking the ball all over the park.
"His average is remarkable. It is not often I have a sympathy for Piers Morgan but I thought he was making quite a powerful argument this morning on my radio.
"But I will let the England selectors pick the England team, I think I had better stay out of this one."
Pietersen was part of the side that were thrashed 5-0 by Australia in The Ashes.