Arsenal will have to up their bid to £12 million to secure the services of Christopher Samba.
The Gunners had originally submitted an offer of £10 million for the Blackburn defender but must pay more to cover the costs of a clause inserted by Samba's former club Hertha BSC.
The deal - signed when Samba switched to Blackburn in January 2007 - means that the German side will get a 15% cut of any sale.
Samba was appointed captain of Blackburn at the start of last season but was stripped of the title in December after he announced his desire to leave.
Spurs are also thought to be a potential suitor.