A £75m signing from RB Leipzig, Sesko has two goals in 11 appearances this season.
"The jury is very much out on him," Pardew told talkSPORT.
"I've not really seen enough from him yet to stick my hat on him and say, 'Wow, this guy's going to be great'.
"It just seems like one of those normal kind of striker bedding-in periods, isn't it? Where he's in, he's out, he's not really getting game time, enough of it.
"The problem with Manchester United of course is when you've got a squad which is built for European campaigns, you've got no Europe.
"So, he hasn't got that quantity of games that perhaps he would like. It's a nice problem for him (manager Ruben Amorim) because he gets to work on the team from Monday to Friday so to speak.
"For Amorim, I think this is probably what he needed this year, just to sort of work on the team, get his ideas across. Sort that energy out in midfield... and get the striker up and running."