Beattie who missed the home game with Norwich a couple of weeks ago meant that Rob Hulse stepped in and did a great job. Hulse then kept his place at Barnsley last Saturday but got substituted for Beattie halfway through the 2nd half.
Blackwell told the Sheffield Star:"Beatts is well aware that he's got a fight on his hands now," Blackwell said.
"Gary Speed, Michael Tonge and David Carney too.
"When I look at the bench and see Ugo Ehiogu and Chris Lucketti then it's pretty obvious that Matthew Kilgallon and Chris Morgan, who I believe are developing a fine partnership, have to keep doing the business too."
Beattie has netted 15 goals so far this season.