Sam Allardyce has lauded Mamadou Sakho's arrival at Crystal Palace for giving his side more defensive stability - but admits a permanent deal for the Liverpool defender would require a "big negotiation".
The 27-year-old France international moved to Selhurst Park on loan in the January transfer window shortly after Allardyce replaced Alan Pardew at the helm.
Sakho had not played for Liverpool all season and had to work on his fitness before coming into the Palace side for the 1-0 win over Middlesbrough last month.
He was also in the team which secured a 2-0 victory at West Brom to take the Eagles out of the Premier League bottom three.
Until that point, Allardyce had lamented his side for their inability to keep clean sheets, specifically after they were hammered 4-0 at home by bottom side Sunderland.
But now he has Sakho, as well as fellow new recruits Patrick van Aanholt and Luka Milivojevic, the former England boss reckons his side are much harder to break down.
"I think two people on this front, Luka & Mama have given us more defensive resilience," he said.
"We are more defensive in terms of the capabilities of looking after the opposition's attacking forces have been improved by those two players and Patrick.
"We have found that we are more difficult to score against which has been one of my first aims, my first targets ever since I first came here.
"Once we began to do that we began to win football matches and three wins out of five have all come because we can keep clean sheets so the basis of our defensive unit has grown and got better and that has been a good way forward for us to get out of the trouble we are in.
"Mama has played a big part in that, as have Luka and Patrick, and the whole team as a whole are defending better."
Sakho will no doubt remain at the heart of the Palace defence when they welcome Watford to south London on Saturday looking to keep out of the relegation zone.
But Allardyce conceded it would take a special deal to convince the former Paris St Germain man to sign for Palace full-time.
"It would be a big negotiation at the end of the season if we were to stay in the Premier League," he said.
"At this moment in time Mama has chosen crystal Palace to play first-team football, I think he has settled into the environment exceptionally well.
"He has worked extremely hard at getting himself fitter because he had not played a competitive game all season and he has shown what a good defender he is, and his capabilities on the ball - in possession he has been exceptionally good."
One player who will not feature against the Hornets is van Aanholt, who is missing with an ankle injury.
Other than the loss of the ex-Sunderland full-back, Allardyce has the same squad that overcame West Brom last time out.