Isak, who arrived from Newcastle United last summer for a club-record fee of 125 million pounds, has endured a frustrating debut campaign at Liverpool.
The Sweden international has made 16 appearances in all competitions but has been sidelined since December after suffering a broken leg and ankle damage in a 2-1 win away at Tottenham Hotspur.
Providing an update ahead of Sunday's Premier League trip to Nottingham Forest, Slot said: "Alex has been on the pitch this week, not with football boots yet but with running shoes. The next step is ball work, then joining the group."
He added: "It will be around the end of March or start of April when he is hopefully back with the team. That does not mean he is ready to start immediately, but it is good to see the rehab going well. That is credit to him and the medical staff."
Slot also revealed that Jeremie Frimpong is closing in on a comeback from a hamstring injury and could feature in next weekend's league fixture against West Ham United at Anfield.
Off the pitch, Slot addressed the issue of racism following allegations made by Vinicius Junior during Real Madrid CF's Champions League win over S.L. Benfica. The incident, which UEFA is reviewing, led to the match being halted under anti-racism protocol.
"In general, you can never do enough," Slot said. "As a football community, we have to do more. The protocol was followed, and that is the first step. I would hope my players would act the same way."
Liverpool head into the Forest clash sixth in the table with 42 points from 26 matches. Slot believes progress is clear.
"We are in a much better place than three or four months ago," he said. "The most simple reasons are our fitness levels and that we are much better at set-pieces."