VEVEY, Switzerland, June 5 (Reuters) - France were not totally convincing in their warm-up games and might have to make do without captain Patrick Vieira but stalwart Lilian Thuram said he nevertheless believed they could shine at Euro 2008. The 2006 World Cup runners-up did not really look like title contenders in a 2-0 win over Ecuador, a 0-0 draw with Paraguay and a 1-0 victory of Colombia in their last matches before heading for Switzerland, where they arrived on Wednesday. On top of that midfielder Vieira is nursing a thigh injury that will rule him out of France's opening Group C game against Romania on Monday in Zurich and might force him to miss the whole tournament. An element of doubt, however, is not too much of a problem for the 1984 and 2000 European champions with a record for defying odds. 'The summary of our three (warm-up) matches is that we don't have many answers,' defender Thuram, the favourite to take over the armband from Vieira, told reporters after the win over Colombia. 'We have our doubts but when we are in that situation it usually makes us play better,' added Thuram, who remembers that a struggle to qualify and a sluggish start did not stop France from advancing to the final of the 2006 World Cup. A mixture of seasoned warriors and exciting newcomers, France are a tough proposition, at least on paper, but will be tested in a group also featuring world champions Italy and the Netherlands. They did not concede a goal in their three matches prior to the tournament but did not score many either, despite clever moves from Franck Ribery, Karim Benzema and Thierry Henry. 'We put up solid performances but we must show more of a killer instinct in front of goal,' Henry said after winning his 100th cap against Colombia. Coach Raymond Domenech, who will make a final decision on whether Vieira stays in the squad on Sunday, is expected to start the tournament with a team similar to the one he fielded for the match against Colombia at the Stade de France. That was a 4-4-2 formation with Jeremy Toulalan taking up Vieira's role as a defensive midfielder and Henry and Benzema paired up front. Several valued members of the French side such as Thuram and fullbacks Willy Sagnol and Eric Abidal have looked below par this season and much will depend on their ability to recapture top form. Another question occupying France's fans is whether the 20-year-old Benzema, this season's revelation with 20 Ligue 1 goals for champions Olympique Lyon, can live up to huge expectations on the big stage. 'I hope we can step up a gear during the tournament,' Domenech told reporters before France left for their picturesque base overlooking Lake Geneva. 'We believe we're ready but only after our third match will we find out if we were better prepared than our opponents.'