Sinclair joined Charlton on loan from parent club Chelsea at the end of February, but the move has proved beneficial to neither party.
Warnock recently confirmed he was monitoring the 18-year-old forward's situation as he looks to bolster his squad for the Championship run-in.
And while the Eagles boss has reaffirmed his interest in Sinclair, he conceded a switch is improbable.
"I spoke to Scott. We would have loved him here because he would have played every week for us," he told Sky Sports News. "He has gone over to Charlton and it has not worked out for him.
"That just shows that sometimes loans aren't all they are meant to be.
"We would love players like that but I think they have got bigger fish to go to really."