Loew wary of Ronaldo threat
Portugal's forward Cristiano Ronaldo controls the ball during a training session at Moises Cicarelli stadium in Campinas on June 12, 2014, ahead of the 2014 FIFA World Cup football tournament in Brazil - by Francisco Leong
The European rivals meet in Group G, which also contains Ghana and the United States.
Ronaldo, the Real Madrid superstar and national team captain, has been battling a knee injury but featured in a 5-1 friendly win over the Republic of Ireland on Tuesday before being substituted.
Loew saw enough to realise that even a half-fit Ronaldo could put the skids beneath Germany when they meet in Salvador.
"If he plays with pace and with the ball at his feet, then it's hard to prevent him playing," said Loew.
"Ronaldo makes some of the best running lines around. You really have to take care of him every minute. The player who will play against him will have to constantly watch where Ronaldo is running."
The Germany coach is, however, aware that Portugal have strength and talent in depth even if they did need to come through the play-offs to make the finals in Brazil after being pipped to an automatic qualifying place by Russia.
"Portugal have got exceptional, classy world-class players like Moutinho, Ronaldo, Pepe, Nani. Both teams have their strengths," he explained.
"Portugal may play perhaps more on the counter-attack, we might play more possession."
As well as worrying about his opponents, Loew also knows that some talented players in his own squad may be disappointed if they are not selected, with the likes of Bastian Schweinsteiger, Sami Khedira, Mesut Ozil and Miroslav Klose all expected to start.
"It's part of my job to make choices. But I need all the players, precisely at this tournament with its extraordinary circumstances. Not belonging to the first-team isn't a punishment," he said.
"This is the reason why for me there are no regular players (players with a guaranteed place in the starting lineup), we have 23 World Cup participants, who must be on high alert every minute."