Germany coach Joachim Low believes Slovakia gave his side a "wake-up call" when they beat the world champions last month.

The two sides meet in Lille in the last 16 of the European Championships on Sunday evening, with Slovakia holding the mental edge following a shock 3-1 win in Augsburg in a warm-up match in May.

Low's Germany go into the contest as heavy favourites but have yet to hit top gear in the tournament. A 2-0 win over Ukraine was followed by a draw with Poland and a narrow victory against Northern Ireland.

Slovakia qualified for the knockout stages after a goalless draw with England and Low knows Germany will need to make better use of possession to seal a victory and continue on in the competition.

"Slovakia is a different opponent than Northern Ireland, it is a lot stronger," he said at his pre-match media briefing.

"They will challenge us. At the end of May we got a wake-up call with the 3-1. The Slovaks will work defensively good, close down the space.

"We will not get many chances. We have 20 players left (to select from) - I've been thinking whether there are one or two changes."

Low cited the 0-0 draw against Roy Hodgson's England as an example of Slovakia's ability - but insisted Germany will do better than the Three Lions when they come up against a side set out to frustrate.

"The Slovaks have a similar quality in the counter attacks as Poland," he added.

"Slovakia is one of the surprises in the first round for me. They have beaten Russia, were unlucky to lose against Wales and played against England to draw.

"Against us in May they have already made a very good game, were brisk, bold and technically adept.

"They have experienced players in the defence but we will find ways to do better than England."

Slovakia coach Jan Kozak insists the friendly win leading into the tournament will not have a baring on this encounter.

"It's a huge challenge for us," he said at his press conference.

"We are fighting with the world champions for a good result. The fact that we beat them in the preparation is one thing.

"Their line-up will certainly be six or seven players who started in that game but it is a very strong team that is playing together a long time and working in top clubs."

Despite not wanting to draw on that shock victory last month, Kozak said his side can spring another surprise - and revealed they have been practising in case of a penalty shoot-out.

"Each team has weaker points," he added.

"We know that without a good (defence) we cannot get a good result. Whenever we have achieved something big it was always with teamwork.

"We have players who can score goals and run matches. We have experiments in training and are not leaving anything to chance - we have even tried penalties."