London - It may look like one of the great mis-matches of Champions League history, but Real Madrid, who won their tenth European Cup last May, cannot afford to underestimate Ludogorets from the tiny Bulgarian town of Razgrad on matchday two this week.
Football is slowly coming to accept that a team who might once have been regarded as amateur actors bumping into furniture on the European stage have the potential to be significant performers.
They may still have been a little-known third division club only five years ago but progress since being taken over in 2010 by Kiril Domuschiev, one of the richest men in Bulgaria, has been spectacular.
Some observers still feared for them after being thrown into a daunting looking Group B with Real Madrid, Liverpool and Basle.
Yet in the opening game at Anfield two weeks ago they were robbed of a draw against the five-time winners only through conceding an unnecessary last-minute penalty converted by Steven Gerrard.
As in the Europa League, coach Georgi Dermendzhiev's side are playing home games at the national stadium in Sofia, some 275 kilometres away, because of the inadequacies of their own 8 000-capacity ground.
That has hardly proved a handicap so far, Valencia's 4-0 success there being the only home defeat in seven European games over the last two campaigns.
Dermendzhiev did admit, however, that his team played "poorly" in Saturday's 3-2 defeat away to Levski Sofia.
Real, meanwhile, were comfortable 2-0 winners at Villareal, continuing their improvement after a slow start in La Liga.
The holders started their Group B programme by thrashing Basle 5-1, which means the Swiss side need to take something from Liverpool's visit, which is also on Wednesday.
They will hope to profit from Liverpool's inconsistency, which continued in dropping two late points in a 1-1 draw at home to their big local rivals Everton on Saturday.
Atletico Madrid, beaten by their neighbours in last season's Lisbon final, lost their opening game 3-2 away to Olympiakos Pireaus and now face another tough tie on Wednesday at home to Juventus.
Juve top both Serie A, with a 100 percent record from five games, and Champions League Group A, Carlos Tevezhaving scored twice in their 2-0 win against Malmo.
Barcelona remain La Liga leaders with a remarkable record going into their Group F tie against Paris St Germain on Tuesday.
They have scored 17 goals and conceded none after a 6-0 success at home to Granada, in which Neymar and Lionel Messi scored five between them.
Barca were less impressive in defeating Apoel of Nicosia only 1-0 a fortnight ago but will be in more confident mood this week than PSG, who although unbeaten in Ligue 1, have won only three of their eight games.
They badly need striker and totem Zlatan Ibrahimovic fit after missing the last two games. Ezequiel Lavazzi is also doubtful and the French champions may have to turn to Edinson Cavani, who scored the goal in an unconvincing opening draw against Ajax.
Ajax visit Apoel on Tuesday, when the remaining groups all feature recent winners of the competition.
Bayern Munich, who beat their compatriots Borussia Dortmund in the 2013 final, visit CSKA Moscow for a match being played behind closed doors after the Russians were punished by Uefa for racist conduct by supporters last season.
In their opening Group E game, the Muscovites were on the wrong end of a 5-1 result away to Roma, while Bayern defeated Manchester City 1-0 with a late goal by the former City defender Jerome Boateng.
The English champions now need to improve on a poor home record in previous Champions League campaigns when they host Roma, who, like Juventus, have won every Serie A game this season.
Group G sees Chelsea's charismatic coach Jose Mourinho return to his native Portugal for the tie with Sporting Lisbon, while Porto, the team he made surprise European champions in 2004, top Group H ahead of their clash with Shakhtar Donetsk.
On Wednesday, England's other challengers Arsenal follow an opening defeat in Dortmund with a home game against Galatasaray, while the Germans travel to Anderlecht.
The night's other matches see Bayer Leverkusen host Benfica and first-day winners Zenit and Monaco meet in St Petersburg.