Gaitan, 24, has impressed for the Portuguese side this season, and some reports have stated that United boss Sir Alex Ferguson has already tied up a deal.
The Argentine has a £38m release clause in his contract, but United will reportedly send Fabio and Federico Macheda in the opposite direction to secure the capture.
"From what I have seen, I have an excellent opinion about Gaitan. I do not know what United's plans are for the left wing, but Gaitan undoubtedly has potential and capacity to play in the Premier League," Quieroz told TSF.
Gaitan has made 43 appearances for Benfica this season.