McLeish, who last week made his third signing of the month by bringing striker Darius Henderson to the City Ground from npower Championship rivals Millwall, watched his side lose 3-0 at home to Watford on Saturday.
The Scot described the performance against the Hornets as "brain dead" as Forest, who were a point shy of the play-off places when McLeish took over at the end of last year, slipped six points adrift of the top six.
"We need some fresh blood," McLeish told BBC Radio Nottingham. "You can see we need a little bit of help. We look one-paced and we could be doing with an injection somewhere in the team.
"We will keep working hard to see who we can bring in over the next few days. It would be nice to make a few additions.
"I tried for a player last week and he chose to go somewhere else, so that was a bit of a blow.
"But we will keep working hard and hopefully we can get the Forest fans some cheer."