Birmingham City midfielder Sebastian Larsson is backing Blues' new additions to be a big hit at St Andrew's and believes they could be the catalyst to a successful battle against relegation.

The Swedish star, who played an integral part in Blues' promotion-winning campaign, has said the arrival of forwards James McFadden and Mauro Zarate, plus full back David Murphy, has given the squad a massive boost ahead of Blues' match at Sunderland on Tuesday night.

Birmingham's FA Cup exit has afforded the squad a rare Saturday off which will give the new arrivals an extra opportunity to familiarise themselves with their new team-mates and the management team.

In the past, Blues' recruits during the transfer window have proven timely acquisitions and yielded excellent results, most notably in 2003 when Christophe Dugarry, Matthew Upson, Jamie Clapham and Stephen Clemence all arrived to ignite Blues in the second half of the season.

The arrivals of Jermaine Pennant and Mehdi Nafti had a similar, but less dramatic, impact in 2005, although Blues had no such relegation worries during that campaign.

Larsson, who joined Birmingham permanently from Arsenal for £1 million almost exactly a year ago, is backing the current recruits to have a major say in the club's destiny this season.

"The new guys are good additions to the squad and have looked very good in training," he said.

"It will not be hard for them to settle in and we have all been impressed with what we have seen.

"McFadden is doing very well and looks a very strong technical player. I haven't seen much of Zarate. I saw him in the reserves against Arsenal the other night and in a couple of training sessions, and he obviously has a lot of ability.

"We need that competition for places because it makes everyone work that bit harder to make sure they are not left out of the side.

"I am sure they are going to have a major impact on our season and play a vital role."

All three should be in contention for a place in the starting line-up at the Stadium of Light on Tuesday although Murphy, a £1.5 million signing from Hibernian, is still working on his fitness after a minor injury.

Larsson was in the Blues side that was pegged back by a late and controversial Sunderland equaliser at St Andrew's in the second fixture of the season and he is expecting another tough test from Roy Keane's side, although the emphasis will be on the hosts to attack on home soil.

"It will be a different game this time because the pressure is on them at home," he said.

"They will have to come out and attack us more than they did in the first game, and it is up to us to capitalise on that.

"Although we have picked up only one point in the last three games, we feel we performed well against Manchester United, Arsenal and Chelsea, and we are full of confidence.

"We are still not in the bottom three and it is important we pick up a few wins in the next few weeks against sides who are around us in the league."

Meanwhile, full back Mat Sadler said he was sad to be leaving St Andrew's but was relishing the prospect of featuring regularly in the first team at Watford after he completed a £750,000 move, rising to £900,000, to Vicarage Road on Thursday.

The 22-year-old had come through the ranks at Birmingham but felt now was the right time for a fresh challenge after he had fallen down the pecking order at Blues.

"Footballing-wise it was an easy decision because I need to be playing regularly, but in every other aspect of my life, with my family and friends being here, it was obviously a lot more difficult," he said.

"Being at Birmingham has been a bit of a rollercoaster for me and I would be happy to still be playing here but that's what happens in football.

"I will certainly miss the club, my teammates and of course the fans but it is a different stage in my life now and a decision I needed to make."

Blues are reportedly running the rule over Honduras international Carlos Costly.

The 25-year-old striker plays for Polish side GKS Belchatow and has an impressive goal-scoring record for the club.