Playing in the same team as Lionel Messi is too stressful for some players because of the Barcelona star's ambition, Juan Carlos Unzue says.
Messi upset the Catalan giants in the summer when he declared his desire to leave, citing the club's failure to compete for the Champions League as a major factor in his decision.
The Argentina international has been a first-team regular for Barca for almost 15 years and remains the dominant force at Camp Nou.
Unzue, who spent three years working alongside the Argentine icon as assistant coach to Luis Enrique, says the 33-year-old's high standards turn out to be too much for many of his team-mates.
"What has kept Messi going has been ambition, and that brings moments of stress with it," he told Marca.
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"He demands that he continues to be the best and as a consequence he always wants the maximum from those around him.
"It doesn't matter if this is team-mates, the coach, the physio or what, it produces great stress on some colleagues who aren't able to shoulder it."
During Unzue's spell as assistant, Barca won the Champions League, Club World Cup and two La Liga titles among other trophies.
The Blaugrana have struggled to compete for the European prize since that era, with Ernesto Valverde and Quique Setien falling short in their spells in the dugout.
Ronald Koeman took charge in the summer and, while they have disappointed in La Liga, they have secured their place in the last-16 of the Champions League.
Unzue believes Koeman has walked into the club at the right time, saying it is more difficult when expectations are high.
"Koeman I think he is managing well with Leo and with the group," he said.
"Entering a club when you have won titles is more complicated than when you're not winning. When we arrived with Luis Enrique, we did it at the right time, after a year in which the team had not won anything.
"That's how it is with Koeman, because he arrives at a very screwed up moment, but if he is not in a very screwed up moment, Barcelona don't make you the coach.
"Barcelona is always difficult, but if you do it in this situation I think the management is simpler, than for example in the situation that Quique Setien arrived after the titles that Valverde won."