Gareth Southgate's side started their maiden UEFA Nations League campaign with a frustrating 2-1 defeat on a night when concerns over their 23-year-old left-back's well-being overshadowed proceedings.
Shaw superbly set up Marcus Rashford's opener on his first England start since September 2015 - an appearance that came just a week before suffering a hideous double leg break in a Champions League tie.
The left-back appeared to suffer another major injury minutes into second half on Saturday, with his head appearing to hit Dani Carvajal's hip before sickeningly bouncing off the turf.
The impact was audible from the stands and led to him leaving on a stretcher wearing an oxygen mask and a neck brace after lengthy treatment.
Thankfully Shaw was walking and talking before the match was out and tweeted he was 'doing fine' that night, but the full-back will return to United today after being concussed against Spain.
A statement from the Football Association read: "Luke Shaw remained at St. George's Park today for further rest and monitoring having sustained concussion against Spain yesterday. He will return to his club tomorrow."