The Polish striker twisted his knee while on international duty this week.
"He's actually been quite lucky and he doesn't feel any pain, and he's already building up his strength again," said his coach Jurgen Klopp.
"It's not likely (that he will play), but I won't rule it out either."
Nevertheless, with his side still in the hunt in the Champions League, and with a DFB-Pokal semi-final tie with Wolfsburg, Klopp may prefer not to take a risk on his top-scorer.
"I think in April, we have more games than there are days in the month," Klopp added.
Should Lewandowski miss out, Pierre-Emerick Aubameyang will lead the attack. The Gabon international has scored 13 goals this season, coming from a deeper position.
And then there is the challenge provided by the forecast spring sunshine, reaching a high of 23 degrees this Sunday.
"It's a huge difference," said Klopp, whose side have been training in temperatures a fraction of that. "The organism has got to change completely."
They have also got to prepare themselves for a side fighting for their lives at the bottom of the table.
"Freiburg have played some good games lately and they have not been rewarded," Klopp said.
"They are going to want to show us that they want to stay in the Bundesliga."
Freiburg are without the injured Vaclav Pilar and Sebastian Freist, but with the newly-capped Germany international Matthias Ginter.
"I hope more than anything that this experience will give him energy and a high level of motivation for the coming games," said Freiburg coach Christian Streich.