Seattle Sounders head coach Sigi Schmid admits he is unsure if Mauro Rosales will be fit to take his place in the starting line-up this week.
"There was definite progress from yesterday," Schmid told reporters at Tuesday's training.
"We're able to localize the injury so we just have to see how he feels tomorrow and keep going, progressing day-by-day."
The Sounders and Real drew 0-0 in the first leg on the weekend and Schmid admits the fact the return tie could go to extra-time may force their decision on rosales.
"Well, you have to think about that," Schmid added. "You have to make sure your starting people have the capability of going 90-plus minutes.
"You don't want to start too many players that you feel can't got 90 minutes because if that's the case then you're locked into some subs and if something unbeknownst happens - somebody gets injured, something you don't expect - then you're in trouble. So that's going to affect our lineup at the end of the day."