The Premier League title favourites were two goals down to the Hornets before launching a second-half comeback to qualify for the fifth round.
Many of City's second string were included from the off at the Etihad Stadium, but manager Pellegrini, while not completely ruling out incoming signings in the coming days, has insisted that it was Watford's desire and not the struggles of his fringe players that led to their half-time deficit.
"We'll see what happens, deadline day is January 31 - it's not our first concern but we'll see what happens in the future," he told reporters.
"I don't have weak feelings about the team based on one half of football. It's normal that the lower division team has a lot of motivation. But the reaction was there and we played a really good second half."
The Citizens have been linked with central defensive reinforcements in this transfer window.