"If there is any possibility we will certainly make the most of it," Schuster told reporters when asked whether van Nistelrooy would be replaced in the squad.
"Ruud's loss will make us more attentive to the market," he added. "Someone important could come in who helps us."
Van Nistelrooy flew to the United States this week and was treated by the surgeon who operated on the same right knee in 2000 when the Dutchman was at PSV Eindhoven.
The 32-year-old has vowed to return next season but Schuster said the Spanish champions will miss him badly until then.
"It's a big blow for us," the German said. "But our big problem is not so much scoring goals as avoiding conceding a lot. We all want him back but we have to move on."
Schuster said he would be using youth player Alberto Bueno to bolster the first-team squad. Bueno played and scored a fine goal in Real's shock King's Cup exit to third-tier Real Union on Tuesday.
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