Liverpool fear Daniel Sturridge is facing a lengthy spell on the sidelines after the striker suffered suspected ankle ligament damage in training.

Sturridge had trained "exceptionally well", according to Brendan Rodgers, in response to being dropped to the bench and criticised by the Liverpool manager in the Merseyside derby with Everton last Saturday. Rodgers was unhappy with the 24-year-old playing 90 minutes for England against Germany with a thigh problem before the derby but those injury concerns have multiplied after Sturridge left Melwood on crutches on Friday.

The Liverpool striker was immediately taken for a scan on his left ankle and, though the full extent of damage may become clear only over the weekend, the club are braced for bad news. Sturridge suffered ligament damage in his right ankle playing for England against the Republic of Ireland in May and it took a punishing personal fitness programme for him to recover inside three months.

Losing Sturridge would represent a serious setback for Rodgers in his attempts to maintain Liverpool's impressive form in 2013 and guide the club back into the Champions League. Last weekend's rebuke aside, the £12m signing from Chelsea has flourished at Anfield and his 89th-minute equaliser at Everton was his 11th goal of the season.

Liverpool are not blessed with goalscorers in the potential absence of Sturridge despite the outstanding form of Luis Suárez since his return from suspension. The summer signing Iago Aspas is close to returning from a thigh injury but has struggled to make an impact since his £7.6m arrival from Celta Vigo.

"We had a good chat this week of where he is at fitness-wise and I just felt last weekend he wasn't fit enough to go into a game of that magnitude," Rodgers said of Sturridge. "He came on and got the point for us and he has had a really good week in training, up until now."

Sunday's visit to Hull City is the first of seven fixtures for Liverpool in December, a schedule that includes away games at Tottenham Hotspur, Manchester City and Chelsea. And, despite the worry over Sturridge, Rodgers believes Liverpool's squad can handle the demanding spell.

"Mentally we are strong," the Liverpool manager said. "I compare the mentality of the team for my first game at West Brom and now. The difference is night and day. I would expect us to last the pace. There is no question of that. We have the determination to do that. Look at our record this calendar year. We are hard to beat. If we're not at our best and winning, we're fighting to the death to get a result. That's something that's in the group that maybe wasn't there when I first came in."

Liverpool's managing director, Ian Ayre, has held talks with Barcelona over the possible January signing of the full-back Martín Montoya, while the Chelsea left-back Ryan Bertrand has also been linked with a move to Anfield. But Rodgers is prepared to give Jon Flanagan a run in the side after the 20-year-old's impressive display at left-back in the derby. The Liverpool manager has warned Flanagan, however, that he cannot allow complacency to creep into his game.

Rodgers said: "I think Jon is ready. I have a huge amount of respect for him and that was the reason I put him in. I have seen a boy who got his chance a few years ago and it is very easily done that you can become complacent. You get a new contract and all of a sudden you have a few bad games and you are out of the team. For me he has never really featured and that is the brutal honesty of it. He has played in some cup games but that is about it.

"I told him this week to think about where he was a couple of years ago when he was in the team and then he was out of it. I said to him, 'Don't play like you have cracked it because you have had a great game in the derby and been man of the match. Go out and prove yourself every single week and, if you do that, you will be all right.'"