Cotterill went out on loan to Swansea in November and became the Welsh club's record signing when the switch was made permanent at the turn of the year. The 22-year-old signed for the Blades from Wigan after an initial loan spell in July 2008 but never became a regular at Bramall Lane.
Blackwell said: "I didn't feel 'Cotts' gave us enough quality often enough. We knew the transfer window was coming up and Swansea made an enquiry so we decided to move him on.
"'Cotts', on his day, was exciting but he didn't give me enough of those so we cashed the money in and got somebody else who may provide more consistently."
Source: Team Talk
Source: Team Talk