Robert Lewandowski has admitted that he is struggling to cope with the heavy workload brought on by Bayern Munich and Poland this season.
With Thomas Muller currently sidelined with a thigh injury and Franck Ribery out with a ligament complaint, the Bavarians are short of attacking options at present.
Lewandowski was substituted late in the first half of Bayern's 2-0 win over RB Leipzig on Saturday after signaling to the bench and pointing to his right hamstring.
Midfielder Arturo Vidal took Lewandowski's place as Bayern played without a recognised striker in the second half, but the Pole insists that his withdrawal was merely a precaution.
Looking ahead to Tuesday's Champions League trip to Celtic, the 29-year-old told Sport Bild: "For me, Glasgow is just as important as the next Bundesliga game against Borussia Dortmund. We have to win. I didn't want to take any risks on Saturday - it felt like cramp. It isn't too bad.
"This season has been really hard for me. I have been playing for Bayern and Poland every three days since it started. No player can play 90 minutes in every game, but at the moment there is no other option. We do not have a back-up in my position at Bayern."
Lewandowski has played in 20 games for club and country since the start of the season, bagging 19 goals in the process.
