With his compatriots, Gary Boucher and Rob Hawkins, both regular members of the first-team squad, Theunissen has had to be de-registered to make way for a new signing, Badshah Khan, a Pakistan Under-21 international.
Do not shed too many tears for Chelmsford, as they are fortunate that their leading goalscorer, Justin King, has a joint British/South African passport, while Chad Mian doubles with Britain and Bangladesh.
The in-and-out-of-form Chelmsford travel to Oxford tomorrow to play the University, who are still seeking their first win of the season.
With the Premier League inactive because of the expected participation in the elite Champions' Trophy in Pakistan, from which England withdrew, the day's leading match features Surbiton at home to Doncaster. The home side has been forced to make their first change of the season. With 16- year-old Kingston Grammar School's James Webber not available because of England under-18 training at Bisham Abbey, Oliver McGinn, son of the former England international Alistair, comes into the squad.
Surbiton will need to keep an eye on Doncaster's Mark Wood, one of only seven players to have topped the 100 mark with National League goals. Stourport, like Surbiton on maximum points, travel to London to play Hampstead and Westminster in what should be a high-scoring game.
A goal tomorrow for Barford Tigers' Dharminder Singh in their away game against Loughborough Students will see him join the exclusive centenary club.