Noussair Mazraoui has been sidelined through injury but the versatile defender has been making progress in his recovery.
During his chat with MUTV's Mark Sullivan after his press conference, Ruben was asked how the squad was looking.
"Really well," he replied. "I had some choices to make [for the weekend's side]. It was hard. I tried to choose the best starting XI, knowing that, sometimes, it's not the starting XI that is going to finish or close the game, so everyone is really important."
There were eight changes to the team named for the Fulham draw for the midweek cup tie at Blundell Park. One of them was in goal, where Andre Onana replaced Altay Bayindir, while Benjamin Sesko made his maiden start in attack.
Casemiro was an unused substitute, while Leny Yoro and Luke Shaw were not part of the matchday squad.
Onana, Tyler Fredricson, Kobbie Mainoo and Joshua Zirkzee received their first minutes of the campaign.
Argentina international Lisandro Martinez remains out as he works to regain fitness, following knee surgery.