Chris Wilder admits more departures are likely to happen in the coming weeks, with a number of players still available for transfer.
Last week, Louis Reed and Samir Carruthers joined Peterborough United and Oxford United respectively, with the former moving on a permanent basis and Wilder admits the squad re-shape will continue.
The manager remarked: "The rise of the football club over the last two years has been quite steep and unfortunately some players get left behind.
"There are always going to be decisions like this and in terms of Louis (Reed) we've covered ourselves yet again."
Wilder added: "We've covered ourselves with a sell-on and we wish him all the best, if he goes well great and if he finds himself playing at League One level, then he'll have a decent career.
"The same goes for the rest of those available for transfer, all the lads have done jobs for us, but we're now looking to bridge the gap in the Championship, moving from a top ten club, to one seriously pushing for the play-offs."