Vulnerable Fledgling Chaffinch

I came across a fledgling/ juvenile chaffinch seeming rather weak & vulnerable in Glasgow city centre. It was in hot sun on the pavement near a busy road. We tried to move it to safety - it let us catch it very easily - but directly across the road was a 15ft fence & a building site on that side so no foliage or safe options nearby.  We tried to find nest / see parents but no luck.

Weighing options we brought it home, it continued to seem weak, heavy breathing but we have encouraged it to lick fluids off a syringe (seed mushed into water) & this am it is brighter, taking food & flew towards bedroom window.  Now awaiting SSPCA helpline opening, we are wondering if we might be asked to take it back to rescue site (still seems unsafe) or to release in safer foliage? It can fly but unsure how far. I realise it might still be dependent on parents...