The left back, who can also play at centre half, joined Portsmouth in February and was an unused substitute in the FA Cup tie at Southampton.
But the Premier League withheld Tosic's registration after ruling that Portsmouth could not sign any more players due to their financial problems, leaving the defender in limbo.
Wigan and Stoke are both reportedly chasing the 26 year old while Ajax and Real Sociedad have made enquiries, but it was Swansea, who made an official approach.
The player's agent is now considering legal action against the FA following the news, which comes as a blow for both player and Paulo Sousa, who would have hoped to include the Serb in his injury-hit squad for tomorrow's match at Nottingham Forest.
Tosic has played 9 times for his county, and featured 22 times for Bremen in 2 years.
This article first appeared on JACKARMY.net.