The Germany international has played an integral role in the European champions' impressive first season under Guardiola so far.
However, Kroos has just 18 months remaining on his contract and the 24-year-old has been linked with a move to Manchester United.
United boss David Moyes was at Borussia-Park to watch Bayern's 2-0 win against Borussia Monchengladbach last Friday, sparking further speculation that the Premier League champions were preparing a bid for Kroos.
Former Barcelona coach Guardiola is eager to keep the player at the Allianz Arena, but knows there is a danger he could move on.
"He is an important player," Guardiola said. "But it can go fast in football. Here today, there tomorrow."
Kroos has already turned down an offer of an extension from Bayern, and told Kicker-Sportmagazin on Tuesday that he would be "unable to rule anything out" with regard to his future.
"I am under contract with Bayern Munich. Actually, there are, (as) yet, no further talks scheduled, I will therefore fully focus on the second half of the season," he added.
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