The Saints striker admitted last week that he believed England manager Roy Hodgson may make a straight choice between him and Carroll for a spot in the squad for Brazil.
Carroll missed the first five months of the season through injury, and according to Allardyce still hasn’t quite got back to his sharpest.
With games rapidly running out it is only likely to further strengthen Lambert’s chances of making the plane.
Carroll moved permanently to Upton Park for a club record £15m before the start of the campaign, but the powerful centre-forward was ruled out until January with a foot problem.
Encouraging performances on his return contributed to an improvement in West Ham's results, but Carroll has scored only twice in his 13 appearances and his form has faded of late.
Allardyce admits Carroll is still catching up after his spell on the sidelines.
“He's not 100 per cent," said Allardyce.
"He's had no pre-season at all, he's worked very hard, but getting into games at this stage of the season after so long out is hard.
"It's hard to get that ultimate sharpness that you need. Hopefully he can find it.
"He looked sharp when he came back. His enthusiasm and the energy from being so pleased to be back with us carried him through, but that catches up with you when you've been out for so long.
"A little bit of fatigue kicks in. We've got to work through it and hopefully he can finish the season by scoring a few goals for us."
West Ham's five senior strikers have netted just 11 league goals this season between them while the club's top scorer is a midfielder - Kevin Nolan with seven.
Allardyce believes the Hammers, currently 12th in the table, would be finishing the season in the top half had Carroll been fit and insists the club need to bolster their attacking options in the summer.
"What we need to do is find an alternative type of front man that scores a few more goals, we'll have to do that," Allardyce said.
"If Andy had been with us all season, we'd be top half, I'm convinced about that.
"Carlton Cole has done a fantastic job but it took him a long time to get going because he didn't join us until after the January window had shut, and Modibo Maiga has struggled since he's been here unfortunately. We would have hoped he'd have done better.
"I'm convinced the front man is the key to how you do in a season, and if we had Andy out on the pitch, match-fit and scoring the goals we know he can with Kevin Nolan, I think we'd be a lot further up the table than we are now."