The defender has signed a 28-day loan and will be available for the Robins’ trip to Port Vale on Saturday.
Oscar Garcia said, “This is a chance of first-team football and that will be a good experience for Lewis and an opportunity for him to play.
“We have no doubt about his quality, but his chances have been limited due to the form of others in that position. The aim is for Lewis to return from his time with Bristol City having benefited from the experience."
Dunk has impressed for the Seagulls’ under-21s recently, scoring against Ipswich Town in the 3-1 win in August but is yet to feature this season.
The 21-year-old has risen through the ranks at Albion, making over 50 appearances for his home town club since 2009.