Jurgen Klopp says he was worried by the prospect of Joe Gomez getting sent off against Manchester City on Thursday night.
Gomez was withdrawn at half time after enduring a miserable evening at the Etihad as the newly-crowned champions were well beaten 4-0.
The England international conceded a penalty for City's opener when he dragged Raheem Sterling to the ground before his Three Lions colleague got the better of him again for the second.
Phil Foden made it 3-0 before the break and an own goal from Alex Oxlade-Chamberlain compounded a tough night for the Reds on their first game since they were confirmed as Premier League winners a week ago.
And with Gomez on a booking and Dejan Lovren and Joel Matip out injured, Klopp was fearful of his centre-back picking up a second yellow to leave him suspended for upcoming games.
Fabinho was moved to centre-half alongside Virgil van Dijk for the second half as Klopp's threadbare options in the middle of his backline were exposed by Pep Guardiola's City.
Klopp said: "No [injury], it was a yellow card.
"I just thought that after he got a yellow and at the moment, we don't know exactly when Dejan will be back.
"Of course, I hope, but I don't have a big number of centre-halves, so I didn't want to see him now get a second yellow and that is why we made the change."
With Matip out for the remainder of the season, Klopp is down to just two fit senior centre-backs at present although Lovren will continue to be monitored ahead of Sunday's visit from Aston Villa.
