Lekgwathi has been a notable absentee for Bucs of late, most recently missing out on a 3-1 victory over Mpumalanga Black Aces in the Telkom Knockout on Tuesday night - a match, which Sangweni failed to complete due to a torn Achilles.
"He (Lekgwathi) will have to start featuring again. He is part of our plans, part of our team," De Sa said after the last-16 tie at Mbombela Stadium.
"He has started training hard again."
Pirates central midfielder Thandani Ntshumayelo was also forced off the field with a recurrence of a metatarsal problem - much to De Sa's concern.
"It's a niggling injury on his metatarsal. He will have to go for another x-ray and scan," said the former Bidvest Wits tactician.
"It is a concern for us. We will hope to get him back as soon as possible."
Regarding the defeat of Aces, De Sa added: "It was a tough game. When we were 1-0 up we should sewn it up but we made a silly mistake just before the (half-time) whistle to concede, and then it was a fight.
"But once again the guys kept on fighting. We hit the post a couple of times and we had to believe."
Bucs set up a quarter-final date with Golden Arrows courtesy of a Lennox Bacela brace, and late strike from Oupa Manyisa, while Mabhuti Khenyeza was on target for AmaZayoni in Nelspruit.