The 21-year-old, who is on loan from German club Union Berlin, hasn’t featured since the Black Cats’ goalless draw at Lincoln in March due to illness.
Dajaku returned to Germany for tests and treatment on what was initially believed to be tonsillitis, but proved to be more problematic.
The wideman is back on Wearside now, though, and was photographed on the Academy of Light pitches on Thursday, when the squad returned to training after two days off.
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When asked about Dajaku last week, Black Cats boss Alex Neil said: "Leon is making progress, he's done a couple of days in the gym.
"He's one that is going to be a little bit longer [in terms of his recovery], because he's not been able to do much of late.
"He's lost quite a bit of weight so we just need to get him back up to speed.
"That's where he's at."
Sunderland have just over a week to prepare for their meeting with Wycombe at Wembley on Saturday, May 21.
The game is likely to come too soon for Carl Winchester, who limped off with a groin issue during the Black Cats’ 5-1 win over Cambridge last month.
When asked about the Northern Irishman ahead of the semi-final matches against Sheffield Wednesday, Neil said: "With Carl, as I said last week that's one where it's going to be weeks rather than days.”