The 25-year-old playmaker is set to seal a big-money move to the Premier League club from Lyon at the start of next week.
However, Moyes is obviously aware of West Ham's ability to always snatch defeat from the jaws of victory and wasn't prepared to get too carried away.
Moyes, speaking after his side's 1-0 win at Aston Villa, revealed: "I understand he's had a medical today as well.
"I can't confirm if it is all good or all bad. I'm obviously really hoping it comes off because I think he is an excellent player.
"He can add something for us and he's another exciting player."
Paqueta would be West Ham's eighth addition of the summer, following Nayef Aguerd, Alphonse Areola, Flynn Downes, Gianluca Scamacca, Maxwel Cornet, Thilo Kehrer and Emerson Palmieri.
"We have brought in several players and a lot are internationals," Moyes added.
"If we bring in a Brazilian international as well, it has been a difficult window but trying to add something at a level that we think can probably keep us up there is what we've tried to do.
"And I have to say I am thankful to the club and the board for trying to get us the best we can."