Juventus boss Massimiliano Allegri has dismissed comparisons between Paulo Dybala and Lionel Messi ahead of his side's blockbuster Champions League clash with Barcelona.

After coming off the bench and scoring in the weekend's 3-2 defeat at Sampdoria, Dybala will start at Allianz Stadium on Wednesday as both sides aim to shore up a top two spot in Group D.

The 24-year-old was questioned for missing two important penalties in October, but Allegri insisted he was not concerned by any slump.

However, the Bianconeri boss was also quick to scupper similarities between Dybala's playing style and that of his Argentina team-mate.

"Paulo is a lot younger and still needs time to develop his game," Allegri told reporters at his pre-match press conference.

"They both use their left foot but they are very different physically and in the way that they move the ball around the pitch.

"Paulo started the season very well, but then he had a dip in form when he missed two penalties. But it's typical to have these ups and downs.

"He will still continue to take penalties for us, as he is still growing as a player."

Juve's loss to Sampdoria left the Italian champions four points off Serie A leaders Napoli and Allegri expects to see greater resolve on Wednesday.

"We have lost two matches in Serie A so I can say that we need to improve our attitude and mentality, especially in the defence, and we need to find the right balance in order to bring the results home," he said.

"Good performances can't always be maintained, so the result is more important than how you play."