Martins scores against Milan in the Champions League in 2003

AC Milan coach Carlo Ancelotti says Inter Milan's Nigerian forward Obafemi Martins will cause a big threat in Wednesday's Uefa Champions League quarter-final derby.

The 20-year-old is set to replace the Brazilian Adriano after a knee injury ruled the prolific forward out of the first leg.

"Martins is fast and unpredictable and very difficult to play against," said Ancelotti.

Martins scored against Milan in the semi-finals two years ago, when Ancelotti's side won on the 'away' goals rule after the tie ended 1-1 on aggregate.

Martins goal not enough for Inter

And the coach is wary of the Nigerian, now that Adriano will miss the tie.

"Adriano is a vital player for Inter. His absence will be felt," Ancelotti said on Tuesday.

"They have (Julio Ricardo) Cruz, who is a very useful player though.

"He is very mobile, works for his team and could be a big help to Martins."

After eliminating Inter two years ago, Milan went on to win the Champions League by beating Serie A rivals Juventus in the final.