Alistair Johnston urged caution and respect after Celtic team-mate Arne Engels was struck by a coin near the end of the 3-0 defeat by Rangers at Ibrox.
There were no Hoops fans inside the stadium due to a dispute about away ticket allocations and the Parkhead substitute fell to the ground as he went to take a corner and had to have treatment before resuming.
Celtic boss Brendan Rodgers confirmed after the match, which left his side 11 points clear of their Old Firm rivals at the top of the William Hill Premiership, that Engels had been hit by a coin and the incident could land the Govan club in trouble with the authorities.
Canada defender Johnston said: “I saw that he (Engels) got hit just above the eye, and it’s an unfortunate situation.
“We’re just lucky that it didn’t hit him right in the eye. No other comment right now.
“I’ve played in some other places in Central America where they throw more than coins at you. You feel pretty safe here.
“Ideally you don’t want anything thrown on the pitch. The words and chants, you get through that, but you just hope everyone respects the players on the pitch no matter who they play for.
“I wasn’t aware (of anything else being thrown) but it’s something that unfortunately happens.
“If that hits him in the eye then it’s probably a pretty serious matter but I would just caution everyone to be smart.
“It’s humans out there, someone’s son, so let’s refrain from chucking things at guys’ heads.”
Rodgers said: “Yes, (he is OK) thankfully – an inch lower, he would have been right in the eye.
“But, yes, I think he’s OK. It’s not obviously great for the game, but, yes, he’s OK.”
A Celtic spokesperson said later on Thursday night: “We understand that Police Scotland are currently investigating two separate incidents.
“The repeated targeting of our players and staff with missiles is quite appalling and completely unacceptable.”
Rangers had earlier issued their own response, with a club spokesperson saying: “Rangers FC condemns this incident in the strongest possible terms.
“The club can confirm it will assist Police Scotland with their investigation.”
