The hooker hardly had any game time in three years at Edinburgh but Glasgow forwards coach Jonathan Humphreys saw enough think he could do a job with Warriors.
Speaking ahead of the Scotstoun meeting with Ospreys, Rennie said: "I reckon George was the best player on the field last week
"He was brutal in tackle and clean-outs. He's very quick for a hooker and did a good job in the set piece.
"Jon Humphreys mentioned him to me, George was playing with London Scottish and on the fringes at Edinburgh, but Humph really rated him.
"I looked at footage and out of that we made a commitment to him. There must be some pretty good hookers at Edinburgh if he hasn't featured for them."