Gennaro Gattuso has changed the face of AC Milan - Andriy Shevchenko

WATCH: Milan's revival under Gennaro Gattuso (0:45)

After a poor start to the season, AC Milan have found new life under Gennaro Gattuso, as they enter the Milan derby on their longest unbeaten run since 2009. (0:45)

Andriy Shevchenko has warned Arsene Wenger his Arsenal players will be facing a rejuvenated AC Milan side that is beginning to resemble their great teams of previous years.

The out-of-sorts Gunners have lost their last four successive games and meet Milan at the San Siro on Thursday night in the first leg of the Europa League's last 16.

In contrast, Gennaro Gattuso's Milan are unbeaten in 13 games in all competitions and have not conceded in their past six.

Gattuso won the Champions League as a Milan player in 2003, playing alongside Shevchenko, and the Ukrainian, who is second on the Italian club's all-time leading scorers' list, feels his old employers have been reborn under the guidance of his former teammate.

"Rino Gattuso has really changed the face of Milan,'' said Shevchenko. "It's almost like two different teams.

"With [previous manager Vincenzo] Montella, Milan signed 11 players and it was a time of transition. It's always difficult when so many players come to find the perfect solution. Any manager needs time to adapt players and bring them into [the] team in the perfect positions.

"The second stage, when Rino came, it has really changed the mentality of the players. Milan are starting to look like the Milan of the old days. They are compact and aggressive and very angry for the win.

"They will be confident against Arsenal. At the moment Milan looks very good.

"The dynamic of the football can change every weekend. If you win you can find something positive. You just keep going and win a couple of games and the confidence comes back. In football things can change quickly.''

As a combative midfielder, Gattuso was renowned for his aggressive nature, once overstepping the mark by pushing then-Tottenham assistant Joe Jordan in the throat during a Champions League game.

Ex-Milan midfielder Ruud Gullit does not believe the 40-year-old has mellowed much in management and feels his style has helped him bring the best out of his players.

"I like him; I like his presence, he's always angry,'' the Dutchman said.

"Sometimes in football you need to be moody. If you love too much then people don't like it.

"I saw them against Roma and they played well. They played with a different system, one striker up top on his own and one floating a bit.

"It's not a team of stars, not one where you identify with certain people but they have become stronger as a team. Arsenal is going to face a good team.''