A high-profile Collingwood coach was sighted taking in Carlton's open training session on Friday as the Blues were put through their pre-season paces at Princes Park.

Magpies assistant Justin Leppitsch -- formerly the Brisbane Lions' senior coach and Damien Hardwick's deputy at Richmond -- was spotted watching on in the nosebleeds of Carlton's home base.

Around 3,000 spectators were purported to have attended Friday's captivating session, as Craig McRae's premiership deputy made up the numbers.

As for the session itself, often-injured defender Zac Williams exerted his influence during Carlton's intense hit-out, per 7News reporter Mitch Cleary's Friday evening report.

After being sidelined for the entirety of last season due to an ACL rupture and managing just nine games the year before, Williams will be hoping to stay available in what shapes as a crucial upcoming campaign for the well-paid ex-Giant.

Meanwhile, athletic hybrid Tom De Koning stated he doesn't want to limit his positional versatility ahead of the upcoming season, declaring his desire to play either as a ruckman or a key position forward.

"I don't want to pigeonhole myself into any position," De Koning told reporters on Friday.

"I'm really open to playing both [in the] ruck and [up] forward."

Fellow ruckman Marc Pittonet was limited to light duties on Friday, while swingman Mitch McGovern spent the entire session away from the main group, and star defender Jacob Weitering remained sidelined with a worrisome calf injury.

The Blues open their pre-season account against Geelong on February 22 in what will be an unofficial match simulation at Princes Park.