But the scan showed a simple calf strain meaning the 20 year-old could return for the League One trip to Plymouth Argyle on August 13. He will definitely miss Saturday’s home game against Morecambe.
Thompson also missed the game at Cheltenham with a knock which has now cleared up.
Relieved Posh boss Grant McCann said: “I didn’t make much of a fuss after the game at Cheltenham, but we did fear it was a serious achilles injury.
"However the scan showed a calf strain so he should be back in 10 days which is a relief for Kwame and us. It was such an innocuous incident. He just shot the ball and felt a sharp pain.
"Nathan Thompson is back training and will be availeble for the Morecambe game. We considered giving him some minutes in the game tonight (at Peterborough Sports), but we had a good training session and he looked good.
"Joe Ward has also shown no reaction to playing 45 minutes at Cheltenham after hardly training for 10 days which is good news as he was brilliant.”