The Dutch champions lost a number of key players in the summer and captain Siem de Jong was, at 24, the oldest player in their ranks during their Eredivisie clash with FC Twente on Saturday.
Former Holland striker Denis Bergkamp, who is now on the coaching staff at the Amsterdam club, has questioned whether there are enough hard men in the team, although Danish holding midfielder Christian Poulsen is set to return at Parkhead.
And Dutchman Petta - who scored in a 3-1 away victory over Ajax that sent Celtic into the group stages in 2001 - feels physicality will be the key weapon for Celtic.
He said: "We had quite a good strong team and had quality all over the place. We could play from the back, from the wings, we could play to the strikers, and we had good midfield players who could make good runs and finish. We had a variety of players.
"If I look at the Celtic team now, there are a lot of players who are very similar. I think they lack a bit of creativity in my opinion."
Petta would not write off Celtic, though, in the wake of Bergkamp's comments.
"Denis knows the values of his team, so I would not argue with that," Petta said. "They are a very young team and they might not be used to the type of football Celtic can play.
"Celtic have to play to their physical strengths."
Petta, who started his career at Feyenoord, added: "Ajax always create chances. They will have a different style from Celtic, they will keep moving the ball about.
"In my opinion it's a must-win game for Celtic. They can't just go for it from the get-go but they have to set their intentions out early and put Ajax under pressure."