Rafael Benítez has painted a worrying picture of John Terry's prospects of regular football at Chelsea, saying the captain is trapped in a "vicious circle" because of a right knee problem which has restricted him since the beginning of November.

The club's interim manager watched his team beat Sparta Prague 1-0 in the first leg of the Europa League last 32, thanks to a late goal from the substitute Oscar, but the post-match discussion centred on Terry, who had travelled to the Czech capital and told Benítez he was ready to play. The Spaniard, though, deemed him to lack the required match fitness and left him as an unused substitute. Benítez appears to be risking a rift with the influential defender.

Terry damaged his knee when the Liverpool striker Luis Suárez landed on it at Stamford Bridge on 11 November and he has since made only three appearances for the club. He suffered inflammation last week, which led Benítez to stand him down from Saturday's home win over Wigan Athletic, and the manager spoke with concern about the stop-start nature of Terry's work, which is preventing him from building momentum and being selected.

"During the [last] week he had a setback," Benítez said. "Then he was fine again [when he returned to training this week] and he had no reaction in the training session. But we have to manage the situation. He has to train more with the team and then he will have more options to play. It's a vicious circle. If he cannot play, he cannot improve his match fitness but, if he can't train with the team, he can't improve his fitness. We have to manage the situation but in the meantime, if [Gary] Cahill and [Branislav] Ivanovic are doing well, we can keep winning games."

Benítez could reflect with satisfaction on Oscar's impact, the Brazilian scoring 28 seconds after his 82nd-minute introduction for Juan Mata, although this was hardly a memorable game or team performance in a competition that Chelsea hardly envisaged contesting when they began the defence of their Champions League title.

"Mata was doing a great job but he was a bit tired," Benítez said. "We needed fresh legs and the quality of Oscar is pretty good because he made a difference." The idea was to keep quality on the pitch and to have fresh legs.

"This is a competition that we have to play now and we talked about it beforehand. It's a European competition and we must realise we have an opportunity to win a trophy. If we progress, they will see that opportunity and it will make a difference. Hopefully we can keep playing well and winning to the end."