Foster is relieved Chelsea opted not to recall Lukaku during the current transfer window.
He said: "I started hearing a few whispers that there was a possibility of it happening especially with the way Chelsea were going and with Torres misfiring.
"It screamed out for him to go back. I think it would have been a huge loss for us. We would have been gutted to lose him.
"He is not only a good asset on the pitch. He is such a good lad to have around the place. He's very level-headed, has no ego to him and is always the last one off the training pitch."