The Saints have already signed right-back Kyle Walker-Peters from Tottenham and centre-back Mohammed Salisu from Real Valladolid this summer.
Everton midfielder Tom Davies is a player they are interested in, but Southampton only want to take him on loan while the Merseyside club would, at the moment, prefer a permanent deal.
"I know we will get players in," Hasenhuttl said. "Now comes the moment where some good opportunities are coming up.
"Our number-one choice, it may not be so easy to get now, but there are some other alternatives coming to us, loan or permanent.
"I think we know we need one or two players minimum, maybe three."