Concrete floor corner missing, new windows

[AlexJA]

Was preparing the area to have new windows installed and when removing the skirting board noticed a corner of the concrete floor missing, any suggestions on how to fix it?

Do plan to have a tredboard wall to wall woth skirting board on top.

 

[Wayners]

I wonder if that hole is the continuation of the ground cavity.
All the houses (1000s) on our estate has some felt layed over cavity at doorways and screed poured over. The result after 60 years is cracking floor along door openings and holes like yours where screed fell though or just wasn't supported.

I've dug mine out a bit. Lined with plastic and poured concrete.

You can read up on how floors are supposed to be done. Not with a cavity along door openings

 

[robinbanks]

I wouldn't bother. There isn't anything you need to do structurally and aesthetically you won't see it when it's re-covered with skirting and flooring