After gleaning four points from the first two fixtures, victory in part one of a double-header against the Basque outfit would set the Reds up nicely for qualification from Group A.
"I feel that this is an important one for us," Moyes asserted. "If we could win this one, it would give us a strong position in the group. We have to go out there and take advantage of the home game and try to get a result.
"I hope it will go to plan. That's what we want to do to put us in a strong position early on."
Sociedad are likely to pose problems at Old Trafford after winning away from home on Saturday, beating Valencia 2-1 at the Mestalla. Antoine Griezmann netted in the first half and Ruben Pardo doubled the lead just before the hour-mark from an assist by Mexico and former Arsenal striker Carlos Vela. Although the hosts pulled a goal back through Dorlan Pabon in injury time, Sociedad still claimed an impressive victory - albeit only their third in all competitions in this campaign.
"I think they're just getting the balance back in the team after selling their best player last season to Real Madrid [Asier Illarramendi]," observed Moyes.
"Maybe they've not started the season how they would have liked but I know that they were unlucky to lose in the last minute against Bayer Leverkusen from a free-kick so they will be hoping to get themselves up and running. We have to make sure we do the job, be professional and try to take all the points in this game."