The 35-year-old, who agreed a one-year contract last summer, has made eight appearances in all competitions so far this season under manager Jose Mourinho.
Carrick is edging closer to United's all-time appearances list after competing in his 430th game for the club in Wednesday night's 4-1 win over West Ham United in the EFL Cup quarter-final.
Mourinho recently admitted that he would like Carrick to stay at the club for "one more season", but the midfielder is uncertain over his future.
"I have said all along I am relaxed about it, but it depends if I am playing and if I am playing well enough, if I feel I can contribute, if the manager feels I can contribute," ESPN quotes Carrick as saying.
"There are a lot of things to be decided. I feel fine. I am enjoying it still. My body is holding up. I didn't know he had said that [about a new contract], to be honest.
"Would I play for someone else? It is not something I am looking to do at the minute. It would be very difficult to play somewhere else. Everyone is different. It depends on circumstance. It depends on a lot of things, but you can't beat that buzz of winning a big game. That is what keeps you going, having success and winning trophies."
Carrick has won five Premier League titles, the FA Cup and the Champions League since joining United from Tottenham Hotspur in 2006.