Kei Kamara will miss Sierra Leone's World Cup qualifier away to Cape Verde on Saturday because of a groin injury.
The United States-based striker aggravated the problem during the 2-2 draw with Group B leaders Tunisia last weekend, a result that leaves them five points behind with two matches left.
"I started feeling the pain during the game and after the game it got worsened and I'm now out of action, Kamara told BBC Sport.
"This means I'll miss our match against Cape Verde and I'm not happy about it as I always like to play and give my best for my country," added the 28-year-old Sporting Kansas City player.
"I'll have to travel this week to the USA to try to cure the injury and I hope I'll not be out of action for long.
"It's an injury I've been coping with as I've been taking some medicines. I'm sure it's hurting me now because I stopped medication after I arrived in Freetown."
Kamara's absence is a huge blow to Sierra Leone, who already had only slim hopes of overhauling Tunisia and reaching the play-off round for Brazil 2014 - Tunisia need only a point to progress as group winners.
That they will now have to attempt to do so without the 2012 Sierra Leonean player of the year makes the task that much harder.
Coach Johnny McKinstry admitted: "Surely we'll miss Kei Kamara because he's an important player, he even scored a goal against Tunisia last weekend and this tells you how important he is in our team.
"We have no option but to play without him and there are other players in the team who can take his place."
Kamara had a brief spell with Norwich City in the second half of last season scoring once in 11 appearances to become the first Sierra Leonean player to score a goal in the English Premier League.
Also missing in the Leone Stars squad are Turkey-based Ibrahim Teteh Bangura, who picked up a groin injury in training, and left-back Sheriff Suma, who is suspended for picking a second consecutive yellow card against Tunisia.
Home-based goalkeeper Ibrahim Tarawallie has been dropped after his error led to the Tunisia leveller in the dying minutes of play.