Lazio coach Simone Inzaghi said that his side had only 13 players available due to injuries and Covid-19 cases for their 1-1 away draw with Zenit St Petersburg in the Champions League on Wednesday.
"It is very satisfying to have a group like this and it is difficult to ask for more," said Inzaghi, who faced a similar problem away to Club Brugge one week ago.
"We played the last two Champions League away games with 13 players; this morning (defender) Luiz Felipe was also having trouble walking, but we are going beyond all expectations."
"It's frustrating to be in these conditions, it's very difficult and we hope to get some players back," he added.
Lazio said before they left Italy that several members of their squad had tested positive for Covid-19. They were not named but Inzaghi said that goalkeeper Thomas Strakosha, midfielder Lucas Leiva and leading scorer Ciro Immobile were among those who stayed behind.
UEFA's official line-up showed 22 players in the Lazio squad although at least half a dozen were from the youth team.
There has been confusion over the tests as Immobile was missing against Brugge and Zenit but played in a Serie A match away to Torino in between.
Italy's soccer federation (FIGC) on Tuesday opened an investigation into Lazio over potential violations of Covid-19 health protocols when carrying out testing. It inspected Lazio's sport centre near Rome and seized the results of swab tests on players.
Before Wednesday's match, Lazio's sporting director Igli Tare said the club had acted in good faith, collaborated fully with the FIGC and suggested there was a difference between Serie A testing and the tests done by European soccer's governing body UEFA.
"There's something that's not right," he told Sky Sport Italia. "In my opinion we need uniformity, only in this way can we move forward. Otherwise, we will be here discussing this every week."