The West Ham forward Matt Jarvis believes the club's progress into the Capital One Cup semi-finals can act as a springboard for an improvement in their league form as they seek to gain reward from Saturday's trip to Manchester United.

Victory at Tottenham Hotspur on Wednesday – their second success at White Hart Lane this season – gave Sam Allardyce's side a semi-final with Manchester City next month, though attention is fixed first on hoisting themselves up the Premier League table. West Ham have been hampered by the absence of Andy Carroll through injury this term and, denied a regular goalscorer, languish 17th and a point clear of the bottom three.

While Carroll nears a return from a persistent foot injury, the club have explored the possibility of taking Robbie Keane on loan from Los Angeles Galaxy – the Republic of Ireland captain spent the second half of the 2010-11 season at Upton Park – before the start of the Major League Soccer season in March. Galaxy would need to be persuaded that the 33-year-old's achilles, upon which he had surgery in November, has recovered sufficiently for him to make the move and the coach, Bruce Arena, is understood to be keener for the player to rest up before the resumption of pre-season training in mid-January.

Regardless of the success of that pursuit, there is optimism that form will pick up and the players and management are encouraged by the resilient display at White Hart Lane. "It was a hard-fought victory and a massive confidence boost for ourselves," said Jarvis, who scored his side's equaliser before Modibo Maiga's late winner. "It doesn't get any better for us, coming away from home against a big rival, than to get a win and play as well as we did.

"I don't think our support for the manager has ever been in doubt. We work extremely hard and show great team spirit. We back the manager and it came out at Spurs. Obviously we just want to keep putting in the performances and getting the right results. I don't see why we can't get anything at Manchester United. Teams have gone to Old Trafford this season and got results. They're still a fantastic side but we go there full of confidence."

West Ham host Arsenal on Boxing Day before fixtures against West Bromwich Albion and Fulham, teams directly around them in the table, complete the festive season. "We've just not been putting our chances away," added Jarvis as he tried to explain his side's toils. "We've created loads of chances and not put them away. We've kept eight clean sheets but we need to score when we get the opportunities. When we get the chances, if we can put them away, it takes the pressure off the whole team defensively."