"We need someone for six months," said Portuguese star Ronaldo, as Real's Argentine striker Gonzalo Higuain had a hernia operation in the United States on Saturday and is unlikely to feature for at least four months.
"There has been talk of some great players such as Ruud (van Nistelrooy) and I'm glad. The more players there are here who want to help this team win the better," said the Portuguese star, who has 22 goals at the half way stage of the season.
Real Madrid dropped to four points behind Barcelona in the championship this weekend where two players at the Catalan club are often on target - Lionel Messi has 18 goals and David Villa 14.
"I want to win lots of Champions Leagues and league titles here," said Ronaldo, adding that Real Madrid could not afford to "go another year without winning something."
Barcelona pipped Real Madrid to the last two Spanish League titles.
Dutch striker Van Nistelrooy, now 34 years old, scored 46 goals in 68 league games for Real Madrid before joining Hamburg a year ago, and pundits feel he presents the best short term solution.
Real Madrid signed French striker Karim Benzema during the summer of 2009 but coach Jose Mourinho recently said that playing with him up front was like going hunting with a cat rather than a dog.
Spanish sports daily Marca maintained Tuesday that Madrid were also in the hunt for Manchester City's Argentine striker Carlos Tevez, but that the aim was to bring in Van Nistelrooy before January 31 when the tranfer window closes.