A finger injury meant the South African recruit was unable to feature throughout the Premiership Rugby Cup and, admitted it was "unexpected" to get the nod from Geordan Murphy for his first Tigers debut after an impressive opening month of the 2019/20 season from Andrew Forysth at outside-centre.
"It was a bit unexpected, Fozzy [Andrew Forsyth] played very awesome in the first four games," Viljoen told LTTV.
"I was all smiles when Geordan told me I was playing this weekend ... I obviously told the family first and they were stoked to see me get my debut."
Speaking in the changing rooms at Sixways, Viljoen admitted the squad were not at their best and needed to improve - quickly - ahead of welcoming the reigning Premiership champions to Welford Road in their next match.
"I don't think we were at our best ... we need to improve going into Sarries next week," he said.
"Credit to Worcester, they came out well ... we need to up our game."
The summer signing refused to make excuses and said there was nobody in the Tigers squad searching for any, especially about a new-look squad needing to find their feet in the new campaign.
"We can't say it is a new team and new season, as we have played four games together," said Viljoen.
"So, that is definitely not an excuse.
"We know each other and we have had a long pre-season together, there is no excuses."
Looking back on the match, Viljoen said the Tigers squad needed to look at less conservative tactics and trust in themselves to force opposition sides under more pressure in upcoming fixtures.
"We need to step up our game individually, physically and take more risks to put the other teams under pressure," said the 29-year-old.
Keeping a lid on things, Viljoen also said the group would remain positive after just one game but not forget the feeling of a disappointing less to help motivate them moving forward.
"It is important to soak it up and feel the loss but on Monday, coming to back training, we have to get our smiles on and be positive," added the Tigers debutant.