Roberto Mancini has revealed the scale of Manchester City's new spending restrictions, admitting for the first time that the club are under pressure to move on players before they can contemplate new signings in the January transfer window.

Mancini has been told that City simply cannot afford another extensive spending programme at a time when their last annual financial figures revealed a £195m loss to increase the sense of a club struggling to fall into line with Uefa's financial fair-play rules.

Ideally the City manager would like to bring in a central midfielder, a centre-half and a striker to replace Carlos Tevez. However, the defender he likes the most, Milan's Thiago Silva, would cost around £30m and, at 27, that automatically rules him out of City's budget.

Instead there is a good chance City will do no transfer business in January other than trying to arrange a deal with either Milan or Juventus for Tevez and offloading fringe players such as Wayne Bridge and Nedum Onuoha. "We need to sell two or three players and then we'll see," Mancini said. "We want to sell first and after that we may have time to buy someone if it's possible. But it's not easy. There are players that could be good for us but every time we want to buy a player their clubs ask for lots of money."

Mancini was smiling when he talked of his transfer targets no longer being approved in Abu Dhabi: "I asked the owner [Sheikh Mansour] for Lionel Messi but it's not possible," he said. But he also believes the new strategy, while necessary, leaves the Premier League leaders vulnerable to the kind of injury issues that have afflicted second-placed Manchester United.

Sir Alex Ferguson has lost his captain, Nemanja Vidic, and the midfielder Darren Fletcher for the rest of the season, as well as having half a dozen other players unavailable. City have not had anything like the same kind of problems, yet Tevez's seven-week strike means they have only three centre-forwards and Kolo Touré's departure for the Africa Cup of Nations in mid-January leaves Mancini with only three centre-halves for potentially a month, one of whom is the relatively inexperienced Stefan Savic.

"This could be a problem in January because we also lose Yaya [Touré] and it will be a big problem for us if we get any injuries," Mancini said. "We have been lucky so far. I'm very sorry [for Vidic and Fletcher] and I hope they can come back quickly. But this is football and sometimes it can happen. For this reason January is going to be very important for us."

Top of the league at Christmas for the first time since 1929, Mancini's team travel to West Bromwich Albion on Boxing Day and face Sunderland at the Stadium of Light on New Year's Day . They could play eight games in January.

Mancini believes Daniele De Rossi of Roma could be available for as little as £5m now he is only six months away from coming to the end of his contract. However, the club's information is that De Rossi's financial demands would put him out of their reach and, even if not, Mancini is not optimistic. "I don't think it will happen, because De Rossi was born in Rome and it's unlikely that he'll leave the city."

City are two points ahead of United and for five out of the past seven seasons the team top of the league at Christmas have won the title. "Usually, yes," Mancini said when asked whether this was similar to his experiences in Italy. "It's a good omen to be top at Christmas but it would be a better omen if United lost their next three games.

"I've told the guys it's possible we could drop to second for three or four games in the new year and maybe go one or two points behind United. But it won't change anything. We know that United have to play many difficult away games and we can recover points in those moments. I think we've got more chance if we have that attitude."