West Brom manager Tony Mowbray described the loss of striker Ishmael Miller for the rest of the season with cruciate ligament damage as "a big blow".
Miller suffered the injury in a collision with Portsmouth keeper David James during the second half of Sunday's Premier League clash at the Hawthorns.
The former Manchester City player was just showing signs of adjusting to life in the top flight with three goals in the last seven matches.
But Albion are resigned to being without Miller for the remainder of the campaign - which makes Mowbray's need to bring in a new striker during the January transfer window even more urgent.
Mowbray said: "It is a blow to us because, while Ishmael is only 21, he is a threat to most teams he plays against with his size, his power and his strength.
"It put teams on the back foot. It was just a collision. He went for the ball with David James and they collided together. It was one of those things."
Mowbray has already admitted he will have to try and bring players in on loan next month or sell to raise funds to buy a player.
He said: "You know our situation with trying to bring players in. We are looking to loan players if we can. We are making inquiries. But it is very difficult to bring in a Premier League quality striker who is going to score you lots of goals on that basis."
Miller has been used by Mowbray as the only central striker in recent matches in a 4-4-1-1 formation with skipper Jonathan Greening operating behind him in a free role from midfield.
Roman Bednar and Luke Moore will now be vying to fill the gap left by Miller in Saturday's crucial league clash with Sunderland at the Stadium of Light.