The 36-year-old felt that something was wrong during his only game appearance this season, September's 4-1 win over Burton Albion in the EFL Cup, and underwent tests to determine the problem.
Carrick underwent a procedure known as a cardiac ablation to resolve the issue and the midfielder claims that he is now healthy, back in training, and focused on making a comeback.
In a statement posted on Twitter, Carrick wrote: "I just want to clear up my situation, as I've had quite a few people asking if I'm OK 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 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."
Capped 34 times by England, Carrick arrived at United in 2006 and has won has five Premier League titles, one FA Cup and a Champions League while racking up more than 400 appearances during his time at Old Trafford.