The cornerback signed a new contract with the NFC East side earlier this year despite missing the last two seasons with knee ligament tears.
Coughlin told reporters: "I think the major thing is to get him on the field, get him practising, bring him along accordingly, and then let him indicate or show us.
"I'm not speculating, he's here for a reason. He's been an outstanding football player, we think he can be again. Of course, we've got to get him on the field. So this is a good start, it'll be slow, but we'll get to that point."
Thomas was a regular starter for the Giants prior to his injuries.