United are the latest English side to be linked with a move for the CSKA Moscow forward.
The likes of Chelsea, Tottenham and Everton are all said to be keen on the Brazilian, but he insists he has not heard anything direct from anyone.
"Until now, I haven't received anything concrete," he said.
"I know about the interest from Everton, Tottenham and Chelsea but this Manchester [United interest] is new.
"I can guarantee that I don't know anything. I just saw the information on Russian TV."