The Championship side have recruited the South Africa international from FC Twente.
Celina is on a season-long loan at Dutch club FC Twente, and the midfielder's performances for the club have sparked Dortmund's interest.
Hakim Ziyech has signed a five-year deal to join Ajax from Twente for a reported fee of €11 million.
FC Twente will play in the Dutch top-flight Eredivisie next season after all, following a successful appeal against a decision to relegate the club.
The Dutch football association's licensing commission has recommended relegating FC Twente to the second tier.
FIFA has imposed sanctions on a number of clubs for breaches relating to third-party influence or ownership of players' economic rights.
Crisis club FC Twente could be a step closer to losing their professional licence.
Even though Hakim Ziyech has been nothing short of sensational for FC Twente, the Dutch club have little choice but to sell their prized possession.
KNVB has banned FC Twente from European competition for three years as punishment for "deliberately misleading" the body about third-party ownership.
Aldo van der Laan said he was leaving because doubts raised by an agreement with Malta-based Doyen Sports Investments were damaging the club.
Mexico internationals Miguel Layun and Jesus Corona have joined Porto, the Portuguese club announced on Monday.
The agent of Mexico international Jesus "Tecatito" Corona said his player is eager to join the ranks of Porto, according to a report.
The Saints have signed the 25-year-old from FC Twente on a two-year deal to bolster their defence as they look set to miss out on Toby Alderweireld.
The Dutch football association has docked former league champion FC Twente three points for the second time this year for failing to meet targets set for their financial recovery.
KNVB set the targets after declaring in April that Twente were classified as being in the highest grade of financial trouble in Dutch football after money problems followed their 2010 title win under Steve McClaren.
Tottenham came from behind to take a 2-1 win in the first leg of their Europa League qualifying play-off against AEL Limassol.
Southampton have completed the signing of playmaker Dusan Tadic from Twente for an undisclosed fee.
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