The former Barcelona coach says he has told his new employers that he wants to bring in the youngster, and that nobody else is being considered for the midfield role
The 22-year-old is one of Manchester United's top targets this summer, and the club have offered to triple the midfielder's wages should he move to Old Trafford.
Thiago has a buyout clause of €18 million [£15m] until July 31 after not playing the required number of minutes stipulated in his contract last season, and United had appeared on the verge of a deal.
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"I asked Sammer and Rummenigge for the player. I don't know what happens in future but I would like to get him," he told reporters.
"Thiago is the only player I want, that's what I told them. It'll be him or no one.
"We have many players but we the need the special [quality] that Thiago Alcantara brings.
"The club will decide. I told them my opinion. [I want him] Because he is from Barcelona. I know him, he is really good. He has been with me at Barcelona B.
"I don't think [signing another midfielder] will be a problem. I spoke to club about my project and told them why I want Thiago Alcantara.
“Nobody will leave Barcelona, unless they feel they won't play much. He wants to play. That's why I proposed him to the club.”