The star halfback's wife Kayla is due to give birth to their second baby this week, however the Warriors have named Johnson to start in the CommBank Stadium match.
Webster confirmed that a call on Johnson playing would be made before Friday but he didn't want to give away any details of what team changes his absence could mean.
"We've got to plan for both scenarios," Webster said on Wednesday.
"We're confident we know what we're doing, but I want Parramatta to have to think about it."
Riding high on the confidence of five straight wins, the Eels will be tough to stop on their home deck with Webster preparing his team for some hostilities.
Sixth-placed Parramatta will be without Mitch Moses in the halves, front-rower Reagan Campbell-Gillard and fullback Clint Gutherson, who have all been picked for NSW in next week's final State of Origin match.
J'maine Hopgood has been listed as the Maroons' 19th man but is likely to be released for the Warriors clash.
Webster's eighth-placed side are smarting after a 28-6 loss at home to South Sydney last round which soured a run of good form.
The Warriors went in off three impressive victories but were flogged in the rain by a well-organised and motivated Rabbitohs outfit.
Webster said that they were fully aware of the key areas that let the side down.
"We didn't get the execution and detail right," he said.
"Our completions are drifting down every week, so we have to win the possession battle and we haven't been doing that."
If Johnson does miss the game, it will delay his 200th appearance for the Warriors. It's one of four milestones that could potentially be reached this weekend, with Dylan Walker set to play his 200th NRL match, Addin Fonua-Blake his 150th and Wayde Egan his 100th.
Webster said the players' celebratory marks gave the side plenty of motivation to bounce back after the disappointing defeat.
"As a club it's really important that we celebrate the milestones, but the most important way is to celebrate with two points," he said.
