During Saturday's 2-1 Premier League triumph over Wolverhampton Wanderers, Jarrod Bowen went down early in the second half and was ultimately forced off in a concerning sight for the away support.
According to West Ham fan site Claret And Hugh, scans have not uncovered any lasting damage, but the England international is said to be suffering from severe spinal bruising.
As a result, Bowen is classed as a major doubt for the trip to the BayArena at the time of writing, and he is one of two fitness concerns for the Europa Conference League winners, who are already set to be without groin victim Alphonse Areola.
Furthermore, Edson Alvarez is suspended on account of picking up three yellow cards in the tournament, so Moyes could be tempted into a formation change, especially with the hosts set to line up with a three-man defence.
Lukasz Fabianski will continue to guard the posts for the Europa Conference League winners, receiving protection from the familiar central pairing of Kurt Zouma and Dinos Mavropanos, who might be joined by Vladimir Coufal in a back three.
Emerson Palmieri's spot on the left is safe, while Coufal's potential inclusion in a three-man backline could see Ben Johnson recalled to the XI in a right wing-back role.
Tomas Soucek was also hooked at the break last time out, but the Czech midfielder will surely be given a shot at redemption in the middle alongside James Ward-Prowse; Kalvin Phillips is unlikely to be trusted in place of the banned Alvarez given his recent horror shows.
Bowen's problem should lead to a recall for Michail Antonio at the tip of the Hammers attack, where Mohammed Kudus and Lucas Paqueta will support him.
West Ham United possible starting lineup:
Fabianski; Coufal, Zouma, Mavropanos; Johnson, Soucek, Ward-Prowse, Emerson; Kudus, Paqueta; Antonio