Gareth Bale has emerged as a major doubt for Tottenham Hotspur's Champions League tie against Milan at San Siro next Tuesday after suffering a setback in his rehabilitation from a back injury.

The Wales international has carried the problem for some weeks and the club sent him to a chiropractor last month, as they feared it was the early stages of sciatica.

The problem flared at Newcastle United on 22 January in the 1-1 Premier League draw when Bale was forced off in the 11th minute. He has missed all three of the club's matches since then.

He was back in light training and slowly stepping up his work with the fitness coaches when he felt a spasm as he started to do some running. The coaches were pushing him a little harder as they targeted the Champions League last‑16 first-leg tie with Milan, but the setback has thrown his participation in that match into jeopardy.

The club hope that Bale will report for the next training session and feel fine but the level of concern is such that good news is unlikely. The club's medics must wait for the spasm to settle before they can put a time frame on his recovery.

Bale has enjoyed a stunning rise to prominence since the beginning of last year, in which he has gone from being a fringe player at Tottenham to one of the most coveted in European football. Internazionale are ready to spark a bidding war for his services in the summer, with a £40m offer to Tottenham, and Real Madrid are also interested.

Bale started in 53 of Tottenham's 54 matches in 2010, with the manager, Harry Redknapp, resting him only for the Carling Cup defeat to Arsenal in September. He also left him out of the FA Cup tie against Charlton Athletic last month.

Redknapp has found it fiendishly difficult to rest Bale, although he has endeavoured to go easy on him in training at times and give him the occasional break. He joked that when he gave Bale four days off at the end of October and told him to get some sun on his back, the 21-year-old went home to Cardiff to stay with his mother.

It has crossed Redknapp's mind that Bale's trouble might be linked to his height, in the same way that Manchester United's Rio Ferdinand and other players with long backs have suffered from sciatic problems.

It would be a bitter pill if Bale were to miss out on playing at San Siro, having lit up the famous old ground on 20 October, when he scored a hat-trick in Tottenham's 4-3 loss to Internazionale in the Champions League group phase.

Redknapp also has selection doubts over the striker Peter Crouch (back) and the midfielders Rafael van der Vaart (calf) and Luka Modric (appendix).