The 21-year-old, who has not started a game for the Championship outfit since December last year, has been called on for defensive cover.
"With the loss of Jimmy O'Connor we needed to strengthen our defensive options," said boss Sean O'Driscoll. "Lewis is a young player who can play at centre-half on the left or right side.
"At 6'4", aerially he makes us stronger, but with the way Brighton play he will be composed on the ball and used to keeping possession."
Dunk has been placed into the squad for tomorrow's clash against Port Vale.