"I always thought when I did leave that I would love to come back one day, the opportunity has now arisen and I feel like it is a good fit at a good time. I am hungry and motivated to do well for the team. I can't wait to get started," said Bale, who will wear the number 9 shirt.
Top seeds Novak Djokovic and defending champion Rafael Nadal, who have first round byes, will begin their campaigns on Wednesday.
The trial will run until the end of October. The situation will then be reevaluated in six weeks.
In the other two games played on Saturday, Tianjin Teda entered the second round with a 2-0 win against Shijiazhuang Ever Bright, Wuhan Zall secured a last 16 round position after defeating Hebei China Fortune 5-4 (tied 1-1 in 90 minutes) after the penalty shootout. Enditem
Polish midfielder Adrian Mierzejewski scored Chongqing's third goal in the 71st minute, helping Chongqing to clinch a 3-0 victory over Qingdao.
The visitors doubled their lead shortly after the start of the second half, when the impressive Gabriel rose highest to head home Willian's corner.
Celta received good news on Wednesday when they completed a move to bring Jeison Murillo back to the club for another season. Murillo was vital as Oscar Garcia's side escaped relegation last season and although the central defender won't play against Valencia on Saturday, his arrival is a major boost for the club.
"To have kept the team together might turn into our big advantage," Borussia's managing director Max Eberl said.
The clash between last season's Premier League and Championship winners was the most eagerly anticipated match of the new campaign's first weekend, and the two sides duly served up a thriller at Anfield.
According to regulations, the last-placed team will be the only one automatic movers. In contrast, the other relegated team and promotion spots will be decided between the 15th place of CSL and the second tier's second place in a two-legged play-off, which will be held in the Suzhou division on November 18 and 22. Enditem
"There was kind of this confusion between the indoor and outdoor record - it's kind of merged. I already had the world record but I wanted to clear everything up and be the best outdoor," said the Swede, who had taken 13 attempts at 6.15m in the season before the night.