Midfielder Danny Guthrie has become Blackburn's third signing of the summer.
Defender Ciaran Clark has signed a new five-year contract with Aston Villa.
David Weir has been sacked as manager of Sheffield United following a dismal start to the season.
Weir was handed his first management job at Bramall Lane in the summer, but his brief reign was cut short after only a handful of games, with the club third from bottom in Sky Bet League 1.
Tuesday's defeat by Hartlepool in the Johnstone's Paint Trophy prompted the board to take action and Chris Morgan takes charge as caretaker manager for the trip to Coventry on Sunday, live on Sky Sports.
The Blades were expected to challenge for promotion this season, but have failed to pick up a victory since the opening day.
Speaking after Tuesday's defeat, Weir admitted that United's form was unacceptable.
"I understand that results haven't been good enough and ultimately that's what I'll be judged on," he said. "It's unacceptable. We need to start playing better and start scoring goals and stop conceding goals.
"I'm a positive person and I look for the positives but I don't think there were any positives at all to take from the game."
Morgan, a former long-serving defender with United, had a spell as caretaker boss last season following the departure of former boss Danny Wilson.