Dec 19 (Reuters) - Austria"s Dominic Thiem will decide by the end of December whether to play at the Australian Open after withdrawing from the upcoming ATP Cup and Sydney ATP 250 events on Sunday due to a long-standing wrist injury. The 28-year-old, who has not played since suffering the injury at the Mallorca Open in June, was unable to defend his U.S. Open title this year and also pulled out of this week"s World Tennis Championship exhibition event in Abu Dhabi. "After speaking to my team we have decided to return to Austria instead of flying directly to Australia," Thiem wrote on Twitter. "Unfortunately, I caught a cold (and tested negative for COVID-19) while in Dubai and was unable to practise last week. "I will therefore not be in the physical condition required to be able to play the ATP Cup and Sydney ATP 250. After not competing for the last six months I can"t take the risk of coming back too soon and picking up a further injury." The world number 15 said his aim was to play at Melbourne Park in the year"s first major, adding that his wrist was "almost at 100%". "Overall, the time I spent in Dubai was great as I have increased the intensity and level of practice... we will make a final decision about my participation by the end of December," Thiem said. The ATP Cup starts on Jan. 1, while the Sydney ATP 250 tournament begins the following week. The Australian Open gets underway on Jan. 17.