The striker met with the Premier League side on Thursday to discuss a possible move and is understood to be on the verge of agreeing a pre-contract deal.
McGhee feels that McCormack should bide his time and weigh up his options thoroughly before making any hasty decisions.
"I think that there will be a lot bigger clubs than Wigan lining up for Ross, and I think he should hold his horses and I think his agent should advise him to do that."
McGhee confirmed that while Motherwell will do everything they can to retain the Scottish Under 21 international they are unable to compete financially with the likes of Wigan and must grudgingly accept that they are a breeding ground for bigger clubs.
"We will be trying to persuade him to stay until he signs for someone else but there is an inevitability about it," he said.
"He has been offered huge contracts at these clubs and we can't compete with that.
"If they have got ability and they come to a place like this, that's on the up, then they have got a chance of moving on.
"Not because they want to play for Motherwell for the rest of their lives but they see it as an opportunity to establish themselves and go somewhere better.
"The fans have a choice, have them for one or two years or not have them at all.
"We cannot compete with Wigan, with Celtic or Rangers, Premiership (English Premier League) clubs. We cannot compete with Championship clubs who are able to pay five and six times the wages that we pay.
"So the fans have to be content that, while they are here, these boys do the absolute best they can and produce performances that entertain them and are committed to them, and when they leave, wish them well."