Bale will undergo a scan on his right ankle, which was twisted in a challenge from David Degen in the dying seconds of the 2-2 Europa League draw against Basle.
Spurs boss Andre Villas-Boas said on Thursday night that he hoped the 23-year-old would be missing for just two games, although the fact that the winger's ankle was bent almost at a right angle to his leg made the injury look a lot more serious.
To say Bale is an important player for Spurs would be a massive understatement. The Welshman has bagged 22 goals for the Londoners this season, many of them truly exquisite strikes.
His performances have meant the likes of ex-Swansea man Sigurdsson, Clint Dempsey and Lewis Holtby have had to spend much of the season on the bench.
The Icelandic forward, who like Dempsey, enjoyed a prolific year with his former club last season, admits Bale's injury is a huge blow, but he is sure Spurs have enough strength in reserve to ensure the team qualify for the Champions League.
"If we are missing Gareth for a couple of games it is a huge loss for us. but there are many players on the bench who are hungry to come in and do well," said Sigurdsson.
"When someone gets injured someone has to step up and fill his place.
"It will not be easy with Gareth because of how well he has been doing this year, but someone needs to come in and do well for the team."
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