Norwich chief executive Neil Doncaster told the club’s website: “We received an offer from Sunderland for Dickson which meets a £1.5m buy-out clause in his contract.
“We are very disappointed to lose Dickson, obviously.
“But the simple facts are that Dickson turned down the offer of a new, more lucrative contract from Norwich City which was already on the table, in favour of Sunderland’s offer.
“We are therefore forced to accept their offer under the terms of his contract.”
