La Gazzetta dello Sport reported that Alberto Paloschi, 18, was to begin training with the first team and could make his debut against Siena in the Serie A on Sunday.
Pato could be sidelined for at least two weeks with an ankle injury.
With veterans Filippo Inzaghi and Ronaldo having just recovered from injury lay-offs and Alberto Gilardino suspended, Milan have problems up front as they strive to clinch a fourth place that secures a berth in the next Champions League.
Pato has begun treatment of the left ankle he sprained on the weekend after scoring the winner, his fourth goal in six games, as the Devils won 1-0 at Fiorentina.
"We'd like to have Pato back for the (Champions League) match in London against Arsenal," vice president Adriano Galliani said.
Beside the home game with Siena, the 18-year-old striker is to miss a mid-week Serie A game with Livorno and an away game at Parma on February 16.
Coach Carlo Ancelotti should have him ready four days later as the seven-time European champions defend their title at Premier League leaders Arsenal in the first leg of the knock-out stage.
As the Champions League looms, Milan also worry about 2007 Golden Ball winner Ricardo Kaka, 25, who has been battling knee problems.
The striker's press agent Diogo Kotscho was quoted as saying that the Brazilian may miss the game against Arsenal although no surgery is necessary.
International Gennaro Gattuso, a mainstay in Ancelotti's midfield package, is also on Milan's injured list with muscular problems, but looks to be in-form for the tie in London.
A pulled muscle, meanwhile, may have grounded Juventus goalgetter David Trezeguet, 30, for a crucial weekend game at Udinese.
Trezeguet, the Serie A top scorer on 15 goals from 21 games, reached the changing rooms limping after Tuesday's training session.
The third-placed Turin side could miss him Sunday in Udine, where international winger Mauro Camoranesi is available having recovered from a pulled muscle.
Star goalkeeper Gianluigi Buffon and defender Georgio Chiellini may remain sidelined as they recover from back pain and a bruised knee, respectively.