However, the midfielder believes they will overcome his departure as they continue their pursuit of Champions League football.
Manuel Pellegrini's side take on Real Zaragoza at La Rosaleda on Sunday in their first match since selling 26-year-old Monreal to Arsenal on Thursday.
And France international Toulalan has backed Malaga, who head into the weekend fourth in the La Liga standings and buoyed by last weekend's 3-2 win at Real Mallorca, to cope without the Spain full-back.
"It's always a shame when a member of the team leaves, but we were quite surprised at Nacho Monreal's exit," Toulalan said. "However, we've dealt with the departure of other players since the beginning of the season, like Santi Cazorla, but we've always overcome any situation.
"With respect to the players leaving, we can't really complain as we've achieved all our goals, and are in a better position than we were last year. We're through to the last 16 of the Champions League and fourth in La Liga, which we weren't this time last year."
United States defender Oguchi Onyewu resumed group training on Friday after recovering from a sprained left ankle, but fellow defender Martin Demichelis was absent following the death of his father.
"The death of Demichelis' father is very hard for us, and difficult in any situation," Toulalan said. "We're confident in our ability, and have done everything we can possibly do up to now."
Ahead of the 1200 (local time) kick-off, Toulalan added: "I've never played in a match with a kick-off as early as midday before. It'll be a bit strange, I think, preparing for a game so early in the day.
"We really need to win this match, to be in a more comfortable position in the league table."
Although they lost Monreal, Malaga did receive a huge boost this week as playmaker Isco extended his contract with the Andalusians until 2016.
Zaragoza's 0-0 draw with Espanyol last weekend extended their winless league run to four games, meanwhile, and coach Manolo Jimenez continues to have selection problems in defence as Cristian Sapunaru's red card in that game means he is suspended for Sunday's trip to Malaga.
Glenn Loovens and Ivan Obradovic are also missing from the back line through injury, while further forward Javi Alamo and Ndri Romaric are unavailable and Franco Zuculini is a doubt with a knee injury.
Jose Fernandez is therefore likely to make a rare league start in their absence, as could Jose Mari should Adam Pinter have to move to centre-back.