Madrid, Sep 12 (IANS): FC Barcelona need to pick themselves up from their shock defeat at home against newly promoted Alaves on Saturday night as they prepare for this football season's Champions League group stage opener at home against Glasgow Celtic on Tuesday.

The Scottish champions can expect to be followed by thousands of fans with their morale sky high after beating bitter city rivals Rangers 5-1 at the weekend; meanwhile in the Camp Nou stadium, it is a moment to reasses matters in the wake of Saturday's defeat, reports Xinhua.

"We will see a Celtic side similar to the one we faced in pre-season. They will push us. To beat Celtic we must be strong in defence, be aggressive and be quick," Barcelona head coach Luis Enrique said, as reported by Barcelona on Twitter.

Enrique rested eight first team regulars at the weekend and saw how his substitutes failed to live up to expectations in a static performance filled with defensive lapses.

"We draw positive conclusions from the defeat against Alaves in order to correct errors," Enrique said.

Sergi Roberto, Gerard Pique, Andres Iniesta, Luis Suarez, Samuel Umtiti and Jordi Alba can all expect to start on Tuesday and Lionel Messi will also be in the side, despite continued worries about a groin injury.

The Argentinean, along with Suarez and Iniesta, came on as a substitute on Saturday and showed no signs of the problem which forced him out of international duty, but the club is aware that it is a problem that needs as much rest as possible.

Tuesday will be the first time the Messi, Suarez, Neymar trio has started this season and Celtic will have to beware given that they have scored a staggering 260 goals between them in the 69 matches they have begun together.

Meanwhile Jasper Cillessen will continue in goal as a result of Marc-Andre Ter Stegen's muscle injury, and will hope for better luck than at the weekend, when Alaves scored two of their three shots on target.

The Dutch keeper was blameless in the defeat, but no goalkeeper likes to lose a game without being able to make an important save, although he will hope for a quiet night in a game which could show whether Saturday's defeat was merely a blip or the symptom of something more serious.

Elsewhere Atletico Madrid have no problems as they travel for their important game away to PSV Eindhoven. Atletico and striker Antoine Griezmann were back to their best in a 4-0 win in Vigo on Saturday and will hope to carry on that form against one of the toughest rivals in their qualifying group.