Sources tell TMZ ... producers for "Building the Band" -- a singing competition series set to debut on Netflix -- were "shocked and saddened" to learn of the One Direction alum's unexpected death.

Liam -- along with AJ McLean, Nicole Scherzinger and Kelly Rowland -- had already wrapped filming the show ... though, the show's premiere date was never announced.

Now, many are wondering if the show will ever see the light of day ... after Liam fell to his death from his third-floor balcony at the CasaSur Palermo Hotel in Buenos Aires, Argentina last week.

We're told producers feel it's "too soon" to make a decision, especially with Liam's costars grappling with their grief.

As we previously reported, Nicole, who served as a judge on "Building the Band" alongside Liam, paid tribute to the British singer on Thursday ... noting it was "such a blessing to get to work" with him.

She added ... "We shared the same love and passion for music and I will forever remember the meaningful and joyful conversations we had."

Nicole was reportedly still in contact with the 1D star -- texting with him on the day he died.

AJ expressed a similar sentiment to photogs earlier this week ... when he praised Liam as a "sweetheart" and recalled how they had "lots of similarities."

Local authorities in Argentina are still investigating the singer's death ... but an initial autopsy report claims he had a mix of drugs in his system at the time he died.