Whitelock has played 88 Super Rugby games, including 38 for the Highlanders, since 2015.
He made his All Black debut in 2013 but it was to be 2017 before he returned to the All Blacks where he captained them against a French XV.
He also captained the Canterbury provincial side leading them to three championships in 2015/16/17.
32 year old Smith debuted for the Highlanders in 2009 and has played 144 games.
The 76 Test veteran will leave New Zealand at the end of the year to play in France.