Kean returned to Juve from Everton ahead of the transfer deadline on a two-year loan deal following the departure of Cristiano Ronaldo, who sensationally joined Manchester United.
Italy striker Kean, who Juve have an obligation to buy, scored 13 goals in 26 Ligue 1 games during his loan spell at Paris Saint-Germain last season and is back in Turin two years after joining the Toffees.
Former Bianconeri striker Vieri believes Juve ought to have tried to lure Argentina international Icardi from PSG.
He told La Gazzetta dello Sport: "Before Ronaldo left, I had said that Juventus' attack is stronger.
"Juve were stronger. Now, I put Inter in front. Cristiano's 25 to 30 goals are gone, those who said it wasn't going well will be happy. When Ronaldo leaves, there are no better options.
"But someone else must score the goals he scored. I don't think Kean will be able to get that many, but I think it's right to give him a whole championship to judge him.
"Icardi is someone who plays little for the team, but he's a finisher by trade, it's easy for him to score 20 goals. Since there's a need for those 20 goals, maybe I would have done more to get him.
"But in the market, it's not always possible to do what seems best."
Icardi has scored 21 goals in 43 Ligue 1 games for PSG, providing five assists.