Sergio Busquets 'emergency option' in Barca's defence - Ernesto Valverde

BARCELONA -- Sergio Busquets is an "emergency option" in defence as Barcelona face a centre-back shortage with just over two weeks to go until the Clasico against Real Madrid, manager Ernesto Valverde says.

With Samuel Umtiti and Javier Mascherano both injured, Thomas Vermaelen and Gerard Pique are the only fit central defenders currently available to Valverde.

Therefore, the Barca coach has had to look for solutions elsewhere, with Busquets playing at centre-back alongside Vermaelen for the final half-hour of Tuesday's 2-0 Champions League win against Sporting Lisbon.

Barca have three more league matches before the end of the year -- including tough away trips to Villarreal this Sunday and Madrid on Dec. 23 -- and can ill-afford to lose any more personnel at the back.

"Busquets in defence is one of the solutions we have if there's a problem," Valverde said in his postgame news conference.

"I didn't want to risk both centre-backs for the whole game [against Sporting] and, in an emergency, Busquets can play there.

"He can mould into any position in midfield but equally he can play as a centre-back. It's not the first time he has played there. It's another option."

With Barca already through to the next round of the Champions League group winners, Valverde made eight changes to his starting lineup from the weekend draw against Celta Vigo.

As well as Busquets, Lionel Messi was among the players to make way to give the likes of Denis Suarez, Paco Alcacer and Aleix Vidal game time.

Denis responded by setting up both goals in an impressive performance, with the first scored by Alcacer and the second an own goal by former Barca player Jeremy Mathieu on his return to Camp Nou.

It was the second successive European game which Messi has started as a substitute, following the goalless draw against Juventus two weeks ago, but Valverde insists he hasn't encountered any resistance from the forward.

"At the end of the day, the players know exactly how this goes and the accumulation of games we have," the coach added.

"My feeling is that it's not that difficult [to leave Messi on the bench]. But, of course, you always think that with him [on the pitch] things are going to go better.

"We know that Leo directs a lot of our attacks. Not just because of his capacity to finish moves, but also for his ability to organise the play and to find those passes that no one sees."

Barca progress into the round of 16 unbeaten in the competition this season and have conceded just one goal in their six games.

"And that one goal was at the very end of our win over Olympiakos here," Valverde pointed out. "That is a consequence of how solid the team is in defence. Normally we defend with the ball, giving little away to the rival. When we have to be together as a unit, we do it well. We're good in that regard.

"Now we are looking forward to the draw. Whoever we get, it won't be easy. In a two-legged game, you're made to pay for any mistakes or bad moments."