The Hornets spent the summer trying to bolster their ranks and, after unsuccessful bids for Tottenham's Tom Carroll and Chelsea's Nathaniel Chalobah, they finally welcomed McEachran to the club on Friday.
Filling the defensive midfield void has been a priority for Zola and England Under-21 international McEachran can play in that role, as well as further forward.
However, despite the latest arrival at Vicarage Road, Zola insists he will continue to scour the market as he attempts to improve his squad.
"A couple more loans would be too much but we might be looking for another player," he told the Watford Observer.
"Things are going well and we are always looking into the situation. If we see a good opportunity then we might do something more but I'm not sure."
The Italian coach added that if he was to add another player it is "likely to be a midfielder".
With Almen Abdi still on the sidelines with a foot injury, McEachran is likely to make his Hornets debut on Tuesday evening as Watford host Premier League Norwich in the third round of the Capital One Cup.