Mark McGhee admits Aberdeen were not "up to speed" over the rule that led to Gary McDonald's red card in the 1-1 draw at Motherwell.

But the Aberdeen manager believes the midfielder's suspension against Rangers is a punishment too far.

McDonald will miss the visit of the Clydesdale Bank Premier League leaders on Saturday after receiving a second yellow card against Motherwell when he lifted his shirt over his face while celebrating his equaliser.

McGhee branded Crawford Allan's decision "ludicrous" immediately after the game but he now accepts the referee was only following rules.

However, he wants suspensions for such offences to be eased.

"I think there has to be rules because there are extremes in situations where players run away with their shirts off," McGhee told RedWeb.

"The other extreme is like Gary McDonald where he pulls the jersey up over his head in front of his own fans.

"It's a difficult one, Gary was unaware that simply pulling it over your face would result in a booking.

"We've got to be up to speed in terms of the rules and we weren't on that one.

"One of the things I think could be changed is when a player is sent off for something like that, I don't think he should miss the next game.

"I think it's perhaps enough of a punishment to be sent off in the game itself."

Meanwhile, McGhee will step up efforts to secure McDonald and two more experienced players beyond the end of the season.

"We're meeting with the agent who represents Mark Kerr, Lee Miller and Gary McDonald on Thursday in Glasgow," said the Dons boss, who is also set to renew his interest in Plymouth striker Steven MacLean.

"Apparently he has been told he can leave Plymouth on a free," McGhee said.

"But free does not always mean free because he still has a contract and if they don't pay up in full, someone else will have to match what he is currently on.

"If Plymouth pay him up and allow him to go, then certainly he is a player we would consider."