Krul was substituted near the end of a 2-1 win in Kazakhstan after falling awkwardly on his knee, but the extent of his injury is still unclear.
He Tweeted: "Gutted to come off with an injury tonight. Thanks for all the get well wishes. I will know more about the extent of the injury after scans ?"
Second choice goalkeeper Karl Darlow is currently out with an injury, so Steve McClaren's side is left with just one senior keeper, Rob Elliot.