No quarter will be given

England's two leading clubs have it all do tonight as six teams chase places in the UEFA Champions League quarter-finals. Chelsea FC and Manchester United FC both enter their first knockout round second-leg ties needing to overturn deficits.

Clean sheet required
Premiership leaders Chelsea take on Primera División counterparts FC Barcelona trailing 2-1 from the first leg at Camp Nou, while United travel to AC Milan needing to score following a 1-0 defeat a fortnight ago. Tonight's other tie, Olympique Lyonnais against Werder Bremen, is less finely balanced with the French champions holding a 3-0 first-leg lead.

First triumph
For all their ambition, Chelsea lack the pedigree of the continent's greatest clubs, although eliminating high-flying Barcelona could set them on their way to a first European triumph since they won the second of their UEFA Cup Winners' Cups in 1998. Barça, the European champions in 1992, provide a formidable obstacle and in Ronaldinho and Samuel Eto'o boast both the World and African Player of the Year.

Ronaldinho confident
Much hype and hyperbole surrounds the fixture, yet Ronaldinho played down the simmering rivalry in an interview with uefa.com. Speaking about Chelsea's first-leg display, he said: "Everyone was saying how good they were before the game, and I thought they were every bit as good as their reputation made out." However, the Brazilian is "100 per cent confident" that his side will progress.

Semi-final victories
Statistics also favour Milan as they tackle English opposition at home leading 1-0. United have twice won the European Champion Clubs' Cup, a tally which could be higher had they not fallen to the Rossoneri at the semi-final stage in 1958 and 1969, while Milan have six times been the toast of Europe, the last time at Old Trafford in 2003. United fell at this hurdle last season, to eventual winners FC Porto, and are desperate to avoid such a fate this time around.

'Humility and caution'
Lyon are overwhelming favourites to triumph in the contest between the French and German champions having won 3-0 in Germany, yet coach Paul Le Guen has called for "humility and caution" from his side. Lyon saw a 3-0 lead overturned at Bremen in the UEFA Cup five years ago but the away team has been knocked out on each of the 69 occasions that such a scenario has arisen in Europe's premier club competition during the last 25 years.

Live coverage
The second leg of FC Internazionale Milano-FC Porto will be played next Tuesday to avoid a clash with Milan-Manchester United as the Milanese clubs share the San Siro. The first leg finished 1-1 at the Estádio do Dragão. As ever this week, uefa.com will bring you all the action live, with text and audio commentaries, and our comprehensive coverage also includes video highlights and full-match reruns.