Witts was listed as "managed" when he was left out of the team for the Suns' victory over GWS last week, replaced by Ned Moyle, and was unable to win back his spot this week.
The 33-year-old will again be an onlooker when fifth-placed Gold Coast (5-3) host the Saints (4-4) in Darwin on Saturday night.
"He'd be hurting, no doubt about it," Collins said.
"He's an AFL-quality ruckman who's not getting a game at the moment.
"I've got full confidence that he'll be playing AFL football again soon and when he does he won't look out of place because we know the type of player and man he is."
Moyle, 24, has only 14 AFL games under his belt and will receive ruck support from key defender Mac Andrew and forward Ethan Read at either end of the ground.
They will have the task of quelling St Kilda's imposing combination of Tom De Koning and Rowan Marshall.
"Moyley's been consistent for four or five years," Collins said.
"It's just the game - there's kind of only one spot for a ruckman and we're blessed to have two exceptional ruckmen.
"Moyley had a great game last week against the Giants and hopefully he continues that for the rest of the season."
Gold Coast boast a strong record at Darwin's TIO Stadium, where they have played two 'home' games in each of the past four seasons and won all eight.
The Suns host successive fixtures at the venue against St Kilda and Port Adelaide over the next week.
"The conditions are very similar to what we face all throughout our pre-season and I think our game style is really suited to it," Collins said.
"Also, as a team and a club, we embrace being up here ... we come here with a really positive mindset and we play good footy off the back of that."
Gold Coast and St Kilda both made just one change to their teams, with the Suns naming second-gamer Ben Jepson to replace Sam Clohesy (suspended).
Brownlow Medal winner Matt Rowell (ankle) is unavailable for a second straight week.
Darcy Wilson replaces Dan Butler (hamstring) for the Saints, who are again without dangerous forward Liam Ryan (corked hip).
St Kilda started the season slowly but have won three of their last four games in a run that included a one-point defeat to Adelaide.
"They're a good team who are playing good footy and their brand stacks up, but we think we can nullify their strengths," Collins said.
"Last week we took a step forward in playing the type of footy that we want to play, so it's going to be a good match-up for us."
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