Messi hadn't played any competitive minutes since suffering an ankle ligament injury in the Copa America final on July 14
The dead also included training centre members, police personnel and civilians. The toll could rise further as some of the injured were said to be in critical condition, Khaama Press reported.
The attack, claimed by the Taleban, took place in Gardez city, 100 km south of Kabul and the capital of Paktia province that borders Pakistan.
The number of attackers was six, all equipped with suicide vests and light arms, according to the security forces.
The provincial police chief who died was identified as Toryalai Abdyani.
The attack began around 9.30 a.m. when a suicide bomber detonated himself outside a police barrack and followed it up with a car bomb, a spokesperson for Paktia Governor Abdullah Hasrat told Efe news agency.
The deafening explosion was followed by gunfire as the militants stormed the police centre and the security personnel fought back.
The number of militants killed remained unknown.
The Interior Ministry said the area was now under the control of security forces and that two of the attackers were killed by the security forces.
In June, six Taleban fighters had attacked the same barracks, killing 11 people and wounding 20.
Over the last two-and-a-half years, the Afghan government has been losing ground to an aggressive Taleban and now controls only 57 per cent of the country, according to the US Special Inspector General for Afghanistan Reconstruction (SIGAR).
SIGAR data also shows that between January and November 2016, at least 6,785 Afghan security personnel were killed and 11,777 wounded, coinciding with an escalation in the conflict.
Messi hadn't played any competitive minutes since suffering an ankle ligament injury in the Copa America final on July 14
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