The champions head into the new campaign without prolific forward Gary Hooper after he sealed a move to Norwich.
The midfielder said: "I think [we need] another striker.
Welsh international Ledley has been linked with a move to Cardiff, the club he quit for the Hoops in 2010.
Ledley admits the prospect of playing in the Premier League is a big attraction for some players but insists his focus is on Celtic.
He said: "It's just rumours at the moment. There has been nothing official.
"A lot of players want to play in the Premier League and that's why they have done pretty well with their signings so far.
"It does attract people but, at the moment, I'm with Celtic and I'm just concentrating on a big week ahead of me."