Forster was previously at Newcastle, and he said last week he would "love to return to St James' Park, and who knows, it may happen."
But not if Sunderland have their way.
Forster still has hopes of making England's World Cup squad, but he understands is chances would be low if he stayed at Celtic, playing in the "One Team" Scottish League.
Mignolet is expected to move to Arsenal for a fee of around £10m, and Forster was only valued at £2m when hev moved to Parkhead.
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