The Hammers qualified for the competition after registering a club record number of Premier League points last season.
West Ham are set to go head-to-head with Dinamo Zagreb, Genk and Rapid Vienna after being drawn in Europa League Group H last month.
Will West Ham progress beyond the group stage?
But the Hammers managed to welcome CSKA Moscow ace Nikola Vlasic in a big-money move and 23-year-old Czech Republic midfielder Alex Kral on a season-long loan, with a view to making the transfer permanent, on deadline day.
Despite an increase in the number of fixtures coming their way this season, Rosser claims Moyes will not be using the Europa League as an opportunity to rotate his squad.
He told TIF: “I certainly don’t think they’ll play weak teams in the Europa League. I think it’s such a big chance for them and obviously earlier in the season you’re able to have a good go at that and it won’t impact them as much as it might further down the line.
“The players are incredibly fit under Moyes. Tomas Soucek, Declan Rice, Vladimir Coufal, Pablo Fornals and Jarrod Bowen can run all week. They can go like there’s no tomorrow.”