The Celtic goalkeeper approached Willie Collum moments before the second half started and ushered the match official to the Copland Road end of the pitch.
Pictures on Sky Sports showed a shard of brown glass and the base of a glass bottle implanted in the turf.
“That is absolutely outrageous,” said Andy Walker. “To see broken bottles on a field of play that can affect the referee, the players or anyone it’s aimed at is absolutely outrageous.”
Both teams had played out an engrossing first half which ended 2-1 in the visitors' favour.
Aaron Ramsey gave Rangers the lead in the third minute but Tom Rogic quickly equalised for Celtic.
A goal from defender Cameron Carter-Vickers two minutes before the interval gave the visitors the lead at the break.