FRASER Gehrig's football future is on a knife's edge after a performance last night that revealed his body was failing him and which his coach, Ross Lyon, admitted was "a concern".

After a seven-touch, single-goal game against Collingwood that admittedly began promisingly, Lyon said he would sit down with the 32-year-old St Kilda spearhead, who retired at the end of last season, only to change his mind and return to the game this year.

"Clearly, it's a concern," Lyon said after the Saints' nine-point loss and Gehrig's fifth outing for the year.

"His body's not what it was, really. And it's frightening what can happen in six months. He's a really proud competitor … but his hand's been worrying him and he struggled to glove it a bit tonight, but I feel I've given Fraser every opportunity over the last few weeks, which really I didn't feel post-Geelong (in round four) that I'd done, and it was important that that's been done.

"So we'll assess his body and his mind, but ultimately, it's what's best for St Kilda. At four (wins)-four (losses), we've got some youth to come in. We've got (Ben) McEvoy in the ruck and we've got Jarryd Allen and (Matthew) Ferguson in the twos.

"We really respect Fraser and wanted to give Fraser every opportunity. Now's not the time probably for me and Fraser to talk about it. But he'll be really disappointed and we'll sit down during the week."

Lyon said he was sure that Gehrig was still hungry to play — "He's a really hard trainer and Father Time catches up with you" — but whether he was still capable of doing that was another matter entirely.

"You all saw the performance tonight and over the last few weeks and Fraser was keen to have a crack at it. And we always said that, at the right time, we'll sit down and review it … I see it as an issue, but until I get to Fraser and talk about it, there's no conclusion either way."

Collingwood and St Kilda had contrasting experiences with the first trial of the interchange bench monitoring system that, in light of the 19th man drama in the Sydney-North Melbourne game in round six, has club stewards controlling the release of players onto the field and AFL officials recording them.

The Magpies had five men on their bench several times and were still struggling with the procedures well into the final term.

"Put it this way, if the rule's going to come in, which it has, I'm particularly pleased you get a week to get it right," Pies coach Mick Malthouse said afterwards, referring to the fact there won't be penalties for contravening the rules until round nine.

But Lyon said, as best he could see, the Saints had adapted instantly.

The Magpies reported no injury problems despite Dane Swan struggling to walk after the game with a leg complaint. Malthouse said it was merely cramp and that Leon Davis, who also appeared impeded late in the game, was also fine.