The maximum number of matches that a team going out of the tournament in the first round itself can win is

In the 1^st round in one group number of matches is (7 x 8/2) = 2
Lets consider bottom 3 they will have 3 matches between them, so remaining 28 - 3 = 25 matches have involvement of top 5 teams, if they won equal number of matches i.e 5 each then decision will be taken based on tie breaker rule, hence a team may be eliminated even after winning 5 matches.