ENGLAND (REUTERS) - Liverpool's injury crisis has worsened ahead of Sunday's Premier League clash with Crystal Palace with defenders Joel Matip, Ragnar Klavan and Lucas Leiva all doubtful due to injury, manager Jurgen Klopp said on Thursday.

They are already without influential midfielders Adam Lallana and Jordan Henderson as they attempt to consolidate their top-four spot that would guarantee Champions League football next season, although the former could be in line to return against Watford on May 1.

"Muscle problems with Joel Matip, (a) little bit with Lucas Leiva. Small problem with Ragnar Klavan, could be also not enough time," Klopp told a news conference.

"Adam (Lallana) is back on the pitch. (He) should be involved next week in normal training.

The manager was less confident about skipper Henderson's chances of recovering from a foot injury before the end of the season.

"I don't know, we will see," he said. "At this moment he cannot train. We have to wait."

Liverpool are currently third in the Premier League, having won five of their last seven games, and have lost just once in 16 games at Anfield all season.

But Klopp believes Sam Allardyce's Palace, who are not yet safe from relegation, are capable of posing an aerial threat for his defence, with former Liverpool striker Christian Benteke leading the line for the visitors.

"When the ball is in the air, Christian is a major threat. We felt it a lot of times here," the German added.

"If we let them cross 50 balls, it's pretty likely he will have some dangerous headers.

"But if you only concentrate on Benteke, you have (Wilfried) Zaha and (Andros) Townsend around him. That is one of the best offensive lines in the Premier League."

Crystal Palace, who are 15th in the league, have won five of their last seven games to move seven points clear of the relegation zone with six games to play.