Madrid - Barcelona will have to wait to find out the severity of the injury suffered by Lionel Messi in their 2-2 draw with Paris Saint-Germain on Tuesday night.
The World Player of the Year put the visitors in front with a trademark left-footed finish seven minutes before half-time, but was withdrawn at the break after pulling up with a hamstring problem.
"The club's medical services have informed that Leo Messi suffered an injury in his right hamstring," said a statement on the club's website.
VIDEO: PSG v Barcelona Highlights
"Tests will be carried out on Wednesday to determine the exact extent of the injury."
And there was more bad news for the La Liga leaders as Javier Mascherano has been ruled out for six weeks after he was stretchered off six minutes from time with a nasty-looking knee injury.
"The medical services of the club confirmed at the end of the game that the Barca number 16 has suffered a tear of the internal lateral ligament in his right knee," said another statement from the club on their website.
"Mascherano was injured in the second-half in an accidental clash with Jordi Alba, who fell on top of his leg.
"If he completes the estimated time out of six weeks, Mascherano will arrive back just in time for the final part of the season."
The former Liverpool man's absence leaves Barca short of fit defenders for the return leg at the Camp Nou next week.
Carles Puyol and Adriano have already been ruled out with long-term injuries, so the inexperienced Marc Bartra or Alex Song will likely have to partner Gerard Pique in defence.