Lolley limped off in pain with a suspected hamstring issue straight after scoring a wonder goal in Sydney's 4-0 elimination final win over Macarthur on Saturday.
The English forward's backend to the 2022-23 campaign was overshadowed by a recurring hamstring injury.
Brattan appeared in some discomfort when he was forced from the field of play late in the second half after a heavy tackle from Jake Hollman.
The loss of the pair would be devastating for Sydney boss Ufuk Talay, whose side will await the results of Sunday's other elimination final to find out who the Sky Blues will face in the two-legged semi-finals.
"Joe felt his hammy go on that extraordinary goal that he scored, it was his standing foot he felt," Talay said.
"Bratts gets a lot of knocks and continues but he must be hurt, it's his ankle, we won't know for the next 24 to 48 hours where they stand.
"We've got our captain and Joe, who is influential in the way we play… they are very important to us.
"We adapted quite well (on Saturday) and we have players who can adapt but I do prefer specialists in their positions."
Sydney will host the first leg of their semi-final against either Wellington Phoenix or Central Coast Mariners on Friday night.
But with or without Brattan and Lolley, Talay was encouraged by the way his side responded to a change in tactics that nullified Macarthur's threat in the final third.
In what may be a hint of Sydney's gameplan going deeper into the finals series, Talay switched to a 5-3-2 formation against the Bulls.
The shake-up allowed Sydney to suffocate Macarthur out of possession and overwhelm them further up the field.
"It gave us a lot of joy and gave us a lot of moments to create 1 v 1 opportunities with Joe," Talay said.
"We had some space with some forward runs and at times we were quite comfortable."
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