As the international break ended, some teams are still reeling from the impact of players returning from playing for their national teams and not being available for matches.
Celtic beat Ross County in the Scottish Premiership on Saturday, but Betis’ league game against Granada will be played on Monday, giving them less time to prepare for the match against the Hoops in midweek.
Pellegrini is critical of the fact that his players had to play three matches while away on international duty, stressing that many of them return with no chance of playing for their club immediately.
The Betis boss complained that the fact Celtic play on Saturday in the league, two days before the Spanish side, gives them an unfair advantage.
“Playing three matches [with their national teams] is too much, the majority of footballers return with little chance of playing”, Pellegrini was quoted as saying by Spanish daily Estadio Deportivo.
“Also, while some games are moved, others are not, which is not good for the competition.
“It seems bad to me to play on Monday as well, Celtic play on Saturday.
“They have 48 hours more to recover and prepare for the game.
“These are small advantages that in the end it is not good to give them.”
The clash between the two teams will take place in Spain and it remains to be seen if Celtic enjoy any freshness advantage during the 90 minutes.