John O'Shea and Gabriel Heinze believe Manchester United will have to be at their best to stop Kaka in their UEFA Champions League semi-final with Milan.
Kaka scored both Milan's away goals in United's 3-2 victory at Old Trafford last week, but O'Shea is wary of other players too.
"Kaka is an outstanding talent," he said.
"We saw that in the first leg and we will have to be on top form to stop him.
"But if we concentrate too much on him, the other Milan players will take advantage, so we have to find a balance."
Heinze realises that if Kaka is kept quiet United will have a good chance of advancing to the final, but he knows it will be difficult to contain the Brazilian.
"Kaka is a superstar. In Manchester, he demonstrated his class," he told the Daily Star.
"I was a spectator in his two goals. The first was impossible to avoid and he made a great play for the second.
"We need to stop Kaka from the very first minute. If we let him dominate the play, we will suffer badly."
Although he is full of respect for Kaka, Heinze feels United's own pairing of Wayne Rooney and Cristiano Ronaldo will provide an even more daunting challenge for Milan's defence.
Rooney netted a stunning winner in the first leg and Heinze believes his form has been a huge bonus over the last few weeks.
"For me, our best news is the resurgence of Rooney for the decisive moments of the season," Heinze added.
"Wayne is sensational and I believe that him and Ronaldo are the best attacking pair in Europe at the moment.
"For me, I look at Rooney with so much admiration - and I know he is prepared for a big night."