Hulkenberg told Auto Motor und Sport: "I only know him from the paddock, but he is an ambitious driver.
"He is still young and wild, but he is certainly fast," he added.
Asked if he is looking forward to being partnered by 23-year-old Sainz, having shared the yellow-coloured garage with ousted Jolyon Palmer until now, Hulkenberg added: "It's ok.
"I will continue to do my own thing."
He admitted he may have an advantage over Sainz at the beginning of their new partnership.
"It's hard to estimate, but of course you always need a certain period of familiarisation. We'll see," said Hulkenberg, 30.
Former F1 driver Roberto Merhi is not so sure his Spanish countryman Sainz should have agreed to the early switch.
"Honestly, going to Renault during the season seems like a mistake to me," he told the Marca sports daily.
"He was doing a great year, and then next year, with the tests and a new season, he would have started with Nico on equal terms."
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