Michael Carrick announces he had a cardiac ablation procedure to treat an irregular heart rhythm
Carrick revealed he had felt something was wrong during his only outing of the season - a 4-1 EFL Cup victory over Burton in September - and underwent tests to determine the problem.
He wrote in a statement posted on Twitter: "I just want to clear up my situation as I have had quite a few people asking if I'm okay and why I haven't been fit over the last couple of months.
"After feeling strange during the second half of the Burton game in September I underwent a series of tests. It turned out to be due to an irregular heart rhythm which has been fully investigated and I had a procedure called a cardiac ablation.
"I had to build up training steadily whilst being monitored closely but I feel fine now. I would like to reassure everyone that I'm healthy and back training hard with the team. I'm building up my fitness and aiming to be back in contention for selection soon.
"Thanks for your support, Michael."