McStay is eligible to become a restricted free agent at the end of the season, as rival clubs already circle with tempting offers for the 26-year-old, who has thrived so far this season.
“It so often happens that when your contract (is nearing its expiry), your form goes through the roof,” Matthews, a Lions board member, said while speaking on Sportsday.
“He’s actually had a terrific few weeks and playing the best he’s ever played I would’ve thought.
“He was always a pretty iffy set shot at goal because of the pressure and stress. He used to get nervous, but after 50 games under the belt he’s a lot more comfortable player.
“He’s been a good player and taken a lot of contested marks, the Lions will be trying their hardest to keep him. I can say confidently he’s happy at the Lions but if the money is big enough, that sometimes can tempt any player.”
McStay has recorded six goal assists for the season, ranking equal-sixth in the league across the opening five rounds and currently ranks elite for marks per game at 6.2.
His goal-scoring agility and ability to take a big grab has proven to be a somewhat rare commodity in the league, and has elevated his status to a potential big-money recruit in the off-season.
McStay has already been linked to an unnamed Victorian club that is keen to lure his services and bring him to his home state.
It was previously reported that the club made an "indicative" and "astronomical" offer, understood to be around the six-year mark by way of contract length and $600,000 by way of monetary value.
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Brisbane will be seeking to go 5-1 from the first six rounds as they face Gold Coast this weekend and look to further imprint themselves as a main contender for the flag with their current crop of players.