Langfield was admitted to Southern General Hospital in Glasgow after reportedly suffering from bleeding on the brain.
The 31-year-old was expected to undergo further tests yesterday, and his employers did not issue any new details on the extent of his condition.
Langfield joined Aberdeen from Dunfermline in 2005 and recently signed a new contract that will keep him at Pittodrie until the end of next season.
Jimmy Calderwood, the manager who signed Langfield for Aberdeen, said: "I met Jamie when he was in Majorca with Scott Severin and Derek Young and he was in fine fettle. He was telling me how happy he was to have signed a new one-year deal and was excited by the prospect of a fresh start at Aberdeen next season under Craig Brown and Archie Knox. We had a couple of problems but Jamie was brilliant for me when I was at Aberdeen and when I saw him last week he was looking the best I had seen him in a while.
"It just goes to show, you never know what is around the corner. I just hope everything works out for him. Luckily, Jamie is a very fit lad and I hope it will count in his favour once the doctors get to the bottom of what happened."