Paul Hartley said: “Simon is going for tests because we need to get to the bottom of it.
“He played in the Under-20s game the other night but had to come off after 20 minutes with breathing problems.
“So he’s got to get blood tests to find out what it is but he is in a bad way. The doctor thinks it could be bronchitis, an infection has got into his chest.
“It’s not good and we don’t know how long he’ll be out for but his health is the most important thing.”