Wilson was injured in Ulster's defeat by Edinburgh on Friday

Wilson was forced to retire hurt midway through the Magners League defeat by Edinburgh at Ravenhill on Friday night.

"It is a massive blow to lose Roger, especially with Stephen Ferris also out," said the acting Ulster coach.

"We made too many stupid individual errors and allowed them to score some soft tries," added Williams.

"We imposed ourselves on them in the first 25 minutes and should have scored two or three tries but too many basic errors cost us dearly.

"The second half was again a story of too many errors and you can't afford to be sloppy when you play rugby at this level.

"Our skill levels need to be higher as some of our passing was very poor and sometimes we were guilty of a lack of concentration.

"In many ways we were the masters of our own downfall and that's what makes it particularly disappointing."

Try-scorer Tommy Bowe agreed that Ulster had made "stupid errors in key areas" and were guilty of "not turning pressure into points".