West Ham have been transformed in recent weeks after a torrid start to life under the Chilean.
West Ham did toil to a late win over AFC Wimbledon in the Carabao Cup in between but it did little to convince the doubters.
But a superb 3-1 win at Everton was followed by another fine display in a 0-0 draw against Chelsea to turn the club's fortunes around.
The East Londoners are a team with momentum and Pellegrini will be hoping to carry that through to the Manchester United match at the weekend with a win over Macclesfield on Wednesday night.
West Ham look to have a very real chance in the competition.
Pellegrini could take a big risk, though, when he rings the changes for the tie against a side who have never lost a penalty shootout in their 144-year history.
With a huge game in Saturday's early kick-off against the Red Devils on the horizon, Pellegrini looks set to make as many as nine changes to the side which started against Chelsea last time out.
Adrian will replace Lukasz Fabianski in goal while Ryan Fredericks will come in for Pablo Zabaleta at right back and Aaron Cresswell for Arthur Masuaku at left back.
Angelo Ogbonna will take the place of Fabian Balbuena at centre back while Carlos Sanchez will come into midfield, probably for Mark Noble.
Robert Snodgrass will replace Felipe Anderson with the record signing likely to be saved for Saturday but Andriy Yarmolenko will start again as he looks to build his fitness and will likely be replaced by Javier Hernandez at some stage.
Lucas Perez looks likely to start in place of Michail Antonio up front.
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