The international was hurt playing for AJ Auxerre against RC Lens on Saturday. In the 74th minute, he collided with Nigerian attacker John Utaka and strained his left ankle and knee. A scan on Sunday, his 24th birthday, confirmed the injury and Boumsong admitted: "I am out for three to six weeks."
With the French season entering its winter break next weekend, Auxerre will hope the player can recover in time for the league restart on 10 January. Their final match before the break comes next Saturday at FC Nantes Atlantique, when fifth-placed Auxerre will look to finish the first half of the season on a high.
Earlier, Boumsong had agreed a five-year contract with Rangers starting next summer, when he will be able to leave French football on a free transfer. Rangers manager Alex McLeish was delighted to secure his services, saying: "It's a good bit of business."
McLeish also revealed that Rangers were close to bringing in English midfield player Michael Brown from Sheffield United FC. "We're waiting to see what's available and it would be nice to bolster the squad in January. We're talking to him and have been cleared to do that by Sheffield and talks are ongoing."
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