Johnson has money to spend after the £1.3million sale of star striker Aaron Mclean to Championship club Hull.
"The squad is looking a bit light, especially in attack, and looks weaker on paper than it has done," said the Londoner. "We are involved in talks with a couple of players as things stand and we hope to be in a position where we know about one of them in the next couple of days."
Posh survived a scare from Walsall to remain on the brink of the play-off places.
Two goals from top-scorer Craig Mackail-Smith made sure Johnson's men recovered from falling behind early on to Alex Nicholls` header before a hotly-disputed strike from Nathaniel Mendez-Laing left the Saddlers fuming. Fellow substitute Ryan Bennett completed the scoring in injury time.
Johnson added: "The players already here put in a very professional performance to come back from going behind.