Enner Valencia, Cheikhou Kouyate and Aaron Cresswell have arrived over the summer but the boss says the club can still afford "one quality player" before the transfer window shuts.
Enner Valencia, Cheikhou Kouyate and Aaron Cresswell have all made the move to Upton Park over the summer as Allardyce looks to improve on last term's 13th-placed Premier League finish.
Another significant signing could be pushed through ahead of next week's deadline according to Allardyce.
"We have the budget for one quality player and that's a possibility before the window shuts," he told reporters. "I think that one more player in the squad and we'd have a good squad this year. Hopefully that's a very fit squad and a squad that produces results. I can't see anyone going the other way at the moment [though].
"Then we have an international window and that's good for us with the injury list. Hopefully some of the injured players recover for when we play Hull City [later this month]."
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Despite the early stage of the Premier League season, West Ham has been beset with a number of injury problems.
Andy Carroll's ankle problem could see him sidelined until the end of November and skipper Kevin Nolan will miss at least a month with a shoulder injury.
Matt Jarvis (thigh), Carl Jenkinson (hamstring) and James Collins (suspension) are also unavailable for Saturday's home clash against Southampton and Allardyce revealed that striker Diafra Sakho is in doubt with a back problem.
"Sakho tweaked his back on Tuesday too so we're not sure if he'll be fit for Saturday," he added. "You don't want to be faced with that many injuries, but we're looking pretty good with the way we're playing."