Webster, 26, has been sidelined with a ligament injury to his right ankle sustained during a hard-fought 1-1 draw at Burnley in February.
The international break was expected to give Webster time recover but the former Bristol City man has been ruled out of the match at second placed United at Old Trafford.
"Making progress," Potter said of Webster. "He's not yet joined the group. It's looking more hopeful for the Everton match. But still a couple of weeks away.
"It was ankle ligaments so it is just a case of building them up and getting the movement of his ankle better and stronger.
"He is doing that work and once I think he's got to a stage where he's happy with that then he can join the team. He has been working hard in terms of his fitness so it is more the ankle and the strength and movement in that."
The injuries to Webster, Burn and March leaves Potter desperately short of options on the left side. Joel Veltman is capable of covering on the left and Potter has also used striker Andi Zeqiri and Polish midfielder Jakub Moder at left wing back.
"It does not make it any easier," Potter added. "That is part of the challenge of managing in the Premier League and working with your team. You have to find a solution.
"There is always a time when you lose a player. We played Liverpool and won and pretty much lost Solly and Webby after that game. Then you have to find a solution, you lose a bit of rhythm and communication as a team while you find the next solution.
"But credit to the players they have done it well. We suffered in terms of results during that period but performances were very good. Credit to them, they have tried to find solutions and we are happy we have found a couple in the last couple of weeks."
Striker Aaron Connolly could however be in contention having recovered from a foot injury picked up on international duty.
Percy Tau is in quarantine after representing South Africa during the international break and Tariq Lamptey (hamstring), March (knee) and Florin Andone (knee) remain out.
Anthony Martial, Marcus Rashford and Mason Greenwood are doubts for Manchester United
Martial missed training on Friday with a reported knee issue picked up on France duty, but Rashford and Greenwood’s chances look more positive after they trained having pulled out of England squads.
Victor Lindelof also missed training with an ongoing back complaint, while Ole Gunnar Solskjaer refused to confirm whether David De Gea or Dean Henderson will start in goal on Sunday.