Barcelona boss Ernesto Valverde admits he is unsure of how best to replace the injured Andres Iniesta in his starting XI.
The 33-year-old attempted to play through the injury before he eventually made way for Andre Gomes in the 36th minute.
And, with Philippe Coutinho ineligible for European competition, Chelsea's visit to Camp Nou could require Barca to repair two key components from the team that started on Sunday.
"He cannot be matched, like Messi. You cannot replace a unique player like him," Valverde said of his captain.
"We are going to wait to see the scan of the injury. It looked like a muscle tear, but we will hope that it is not so serious.
"He knows how to manage himself. He was having a great game."
[INJURY NEWS] @andresiniesta8 has a hamstring injury in his right leg. More tests are needed to find out the extent of the problem #BarçaAtleti pic.twitter.com/2rhv79AekT — FC Barcelona (@FCBarcelona) March 4, 2018
Iniesta's early withdrawal against second-placed Atleti was ultimately softened by a victory that improved Barca's lead in La Liga to eight points with 11 matches remaining.
Lionel Messi netted the winner with a sublime first-half free-kick, his 600th career goal for club and country.
"There is no player like Messi in the world," Valverde said.
"I do not know what would have happened if he was playing for Atletico. I don’t want to imagine it, either."