Foley will be allowed to move on, with Motherwell linked with the midfielder.
Saints won 5-1 at Dundee United on Wednesday to give their Scottish Premiership top-six hopes a major boost and Goodwin is looking at strengthening their squad for the push.
"We are working hard on a couple at the moment," he told SMTV.
"I think we need a left-sided defender, there is no getting away from that, the back four is full of right-footers.
"And if we can get another attacking one, then brilliant."
Foley was a key player for the Buddies last season but has found himself sidelined by the likes of Ethan Erhahon, Cammy MacPherson and Jake Doyle-Hayes.
"Sam is 34 now, he's got a wife and a few young kids who are depending on him," Goodwin said.
"I had a good, frank conversation with him about next year, I told him there wasn't going to be an offer from ourselves and that I wouldn't stand in his way if he had the opportunity to go elsewhere and win a contract. I think it's the right thing to do.
"Sam was outstanding for us last season. This season he didn't start as well as we would have liked and that's why he came out of the team.
"He had a couple of really good games at centre-half, but we've got to be fair to the younger ones in the squad.
"We are a club that likes to promote from the academy and we need to make sure that pathway is clear.
"Some of the younger ones have got in, the likes of Ethan, and Cammy MacPherson has been in and out. And we have a young boy in the academy, Dylan Reid, who has been up training with us from time to time and he is one we are really excited about.
"I just feel if I hang on to too may experienced players then it blocks that pathway for some of the younger ones.
"Wherever Sam ends up we wish him well, he will always be welcome at St Mirren."