AC Milan have no margin for error in the second leg of their Champions League tie against Sparta Prague tonight, coach Carlo Ancelotti has warned.

The European champions failed to capitalise on a raft of scoring chances in the first leg, which they drew 0-0, and cannot afford to concede an away goal at the San Siro Stadium.

"On the basis of our performance in the first leg, Milan start as favourites. We're in excellent shape, but the match is still finely balanced," Ancelotti said.

"Sparta are quick on the counterattack and dangerous away from home, even if we know them a little bit better now than we did before.

"We need to concentrate, especially in defence. The first leg result means we can't relax."

Milan have dominated their domestic rivals this season and lead Serie A by five points after winning 10 of their last 11 league matches.

That form has not translated into supremacy in Europe, however, where they lost to unfancied Belgian team Club Bruges and Spain's Celta Vigo in the group phase.

Milan will start without Dutch international midfielder Clarence Seedorf, who suffered a thigh strain during Milan's 3-1 win over Sampdoria at the weekend.

Still, Ancelotti said he felt optimistic of progressing to the quarter-finals: "Of course, the final result will remain uncertain right to the end, but that's the way it'll be in all our Champions League matches from now on."

Meanwhile, Monaco can count on in-form Fernando Morientes to overturn a 2-1 deficit as they host Lokomotiv Moscow.

The Ligue 1 leaders, who beat En Avant Guingamp 3-1 last Friday, will be without playmaker Ludovic Giuly, who has a foot injury, and centre back Sebastien Squillaci, who has a leg problem.

Lokomotiv welcome back South African left back Jacob Lekgetho from suspension, but they will miss influential midfielder Dmitry Khokhlov who damaged his back in the first-leg victory over the French side.

Defender Dmitry Sennikov remains doubtful after breaking his nose in the first leg two weeks ago and missing last Thursday's 1-1 draw against Rubin Kazan in the Russian Cup.