Witts' minor hiccup added to what coach Nathan Buckley admitted was a bad run of injuries for the Magpies in the first eight weeks of the season.
The club revealed on Tuesday that star midfielder Dale Thomas would need surgery on the ankle he injured against Hawthorn in round three.
Thomas had returned in that game from a different injury to the same ankle.
Last year's best and fairest, Dayne Beams, is also out until at least the bye after he was unable to increase his training load as required due to a nagging quad injury.
Recruit Clinton Young is yet to appear for the Magpies while Alex Fasolo had surgery on Tuesday to repair a navicular fracture that will cause him to miss the rest of the season.
Captain Nick Maxwell and Darren Jolly also failed to train on Tuesday but Buckley said their absence was due to the six day break.
Buckley said the decision to opt for surgery on Dale Thomas's injured ankle was made in the hope the Magpies would have a fully fit list available at the business end of the season.
He admitted that although there were "massive reservations and fears" about whether Thomas would in fact get back on track before the season ended, the best course of action was being taken and the club had to accept the reality of his temporary absence.
Thomas will go on the long-term injury list with the Magpies hopeful he may be fit enough to return in round 20.
"It's a tough game and it tests you. You need to be mentally and emotionally tough to be able to handle that," Buckley said.
"'Daisy [Thomas] has shown over a long period of time that he is a tough footballer, he's a tough person and he is going to need all of that and the support of his teammates, as will all of our players for that matter and that is where the strength of the team environment comes up," Buckley said.
Collingwood has Heath Shaw returning from suspension and several players performing well in the VFL.
JacksonPaine kicked five goals for the Collingwood VFL side against Geelonglast Saturday but Buckley said he needed to put in a few consistentgames in succession to force his way into the team.
"He has beenhitting the scoreboard, kicking his two or three every week, but thereis some areas Jackson's aware of that he needed to attend to and wedefinitely saw a spike in that on the weekend," Buckley said.
Buckleysaid it was a matter of time before players got their chance butadmitted that performances such as the win against Geelong made it toughfor players such as Alan Didak and Ben Johnson, who returned frominjury last week, to force their way in to the team.
Collingwoodwill play defending premiers the Sydney Swans at the MCG. The Magpieslost to the Swans in last year's preliminary final and Buckley said therecollection of that game still hurts.
"That night still burns a little bit in the back of the psyche," Buckley said.
