Liverpool have offered £250k but United are holding out for more for the England U21 international.
Benitez said: "We have had many offers from agents to sign young goalkeepers but we are looking for an experienced goalkeeper.
"We have two good keepers here and Chris Kirkland will be back in three months. We want to sign someone on loan instead. It's not likely that we will be signing Scott Carson now."
The teenager was left out of the reserve's against Middlesbrough on Wednesday, adding to speculation that Liverpool were set to make a move.
Carson has failed to respond to last week's improved contract offer from Leeds and Kevin Blackwell confirmed last night: "Scott was not injured, I chose not to play him in the reserves. There has been a lot of speculation about Scott and we daren't risk him because of that. I badly want Scott to stay, but if he is to leave I would not want to jeopardise any possible move by him getting injured."