David Moyes says Declan Rice's return can help West Ham stop leaking goals and get their push for the Champions League places back on track.
West Ham have not kept a clean sheet in their last six games — conceding 12 goals in the process — and face Burnley on Tuesday night after back-to-back defeats.
Rice has missed the last four matches after suffering a knee injury on England duty in March, but is pushing to face Burnley.
'Mostly it is not having Declan Rice,' Moyes said when asked about his side's recent poor defensive record.
'Is he that important? I think so, yeah. He is incredibly important. We've had him back training a little bit. He's made good progress, we're happy and he's ahead of schedule. We'll try to keep pushing him.'
Consecutive defeats by Chelsea and Newcastle have hurt West Ham's push for a finish in the Premier League's top four.
But Moyes believes they can be in the race until the end of the season.
West Ham face Southampton on the final day and Moyes said: 'If we could get the supporters back with European football a possibility, it would be great.
'Nothing would give me bigger pleasure than to tell the West Ham supporters, 'Let's get ready, we're going around Europe'.'