The 28-year-old midfielder suffers from ulcerative colitis, a chronic bowel condition, and featured only 10 times for the first-team last season, his final appearance coming against Benfica back in November.
| MANCHESTER UNITED LATEST
|9/4||Manchester United are 9/4 to win the 2012-13 Premier League with bet365
"It's not really an option, I just want to keep playing," Fletcher told reporters.
"I know someday I will be back. I'm only 28 years old and to talk of retirement, I'm not really thinking about that. I want to give myself every opportunity to get back.
"I've not started training yet but I'm just listening to the doctors and just taking my time really.
"It's so difficult to talk about because it was such an unexpected illness. I just have to take each day as it comes and at the moment I feel like I'm capable of coming back, then I'll try and come back."
After being pipped by bitter local rivals Manchester City to the Premier League title last season, Fletcher is adamant that the league remains the club's main focus going into the new campaign.
"We feel the same every season, just try and win the league," he insisted. "Champions League maybe. We'll try and win every cup we go in but the main priority is the league.
"Obviously after Man City won the league it gives us extra incentive to win it back."