The Black Cats forward tore his anterior cruciate ligament in a Premier League match against Leicester City last December, leading to a lengthy rehabilitation period.
But the 23-year-old will play 45 minutes for the Black Cats' Under-23 side against Manchester City this weekend.
Manager Simon Grayson has no plans to rush Watmore back into the first team despite Sunderland's recent problems in front of goal.
"That's a big boost for Duncan and ultimately us as a club," said Grayson.
"But we're certainly not in a position where we're going to throw him back into the first team.
"He's been out for such a long time and we have to be very careful with that."