WARSAW, Nov 18 (Reuters) - Polish President Lech Kaczynski is in hospital with an infection and has cancelled all engagements this week, including plans to attend a meeting of European Union leaders, his office said on Wednesday.

"The president underwent tests yesterday in hospital and he may leave as soon as today if doctors decide that he can," a presidential press officer said.

Kaczynski's official website said he had cancelled this week's engagements on the recommendation of his doctors. Polish media said his condition was not serious.

Kaczynski, 60, a conservative eurosceptic, had been expected to attend talks in Brussels later this week aimed at choosing a new president of the European Council and a foreign minister for the 27-nation bloc, posts created under the new Lisbon Treaty.

Polish Prime Minister Donald Tusk, Kaczynski's arch rival and likely adversary in a presidential election due next year, is set to attend the Brussels talks.

Opinion polls show that Kaczynski, in office since 2005, is much less popular than Tusk. A survey by CBOS published on Wednesday showed only 24 percent of Poles positively assessed Kaczynski's performance against 62 percent who were critical. (Reporting by Gabriela Baczynska, writing by Gareth Jones; Editing by Elizabeth Fullerton)

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