Alcacer's 59th-minute goal saw Valencia to a 1-0 win over Ludogorets on Thursday, completing a comfortable 4-0 aggregate victory in the UEFA Europa League last 16 tie.
The 20-year-old striker has scored six times in 10 La Liga starts this season, and his form has seen him linked with the likes of Arsenal.
Pizzi was full of praise for Alcacer after his side's win at the Mestalla and feels the Spaniard is among the world's best.
"You'd be hard pressed to find a player in a better rhythm than Alcacer," he told a news conference.
"He's at a higher level than any other comparable player in the world, save for Messi and Cristiano. It's invaluable to have a player in his type of form."
Alcacer headed in the second leg's only goal just before the hour-mark, cleverly placing his effort into the bottom corner from Federico Cartabia's cross.
Pizzi said he was unfazed by who his side will face in the quarter-finals, with the likes of Juventus, Porto and Lyon in the last eight.
"I have no preference on who we face," he said.
"There are teams with long histories and are powerful opponents. Personally, I don't care.
"It will be difficult no matter who we play. I think all four pairings will be great."
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