Morocco, warming up for the World Cup in Qatar in November, had beaten Chile 2-0 in Barcelona last Friday and came close to another success against South American opponents at Real Betis' Benito Villamarin Stadium.
They had the ball in the Paraguay net midway through the second half, only for the effort by Ryan Mmaee to be ruled offside.
They also had to battle to keep a clean sheet in a fast tempo game as Paraguay's Miguel Almiron threatened their goal on several occasions.
It was a second game in charge for new Morocco coach Walid Regragui, appointed earlier this month to replace Vahid Halilhodzic, who was fired following a dispute over the selection of Hakim Ziyech.
Ziyech had been left out of Morocco's team after last year being accused by Halilhodzic of feigning injury to skip playing friendly matches.
The impasse between the Chelsea forward and the national team coach saw him miss the World Cup qualifying campaign and the Africa Cup of Nations finals at the start of the year.
But pressure on Halilhodzic to restore Ziyech to the team, and no reconciliation between the pair, led to the coach being fired last month.
Regragui drafted Ziyech straight into the starting lineup on Friday and he played again against Paraguay on Tuesday.
"It is hard to understand how anyone could leave out a player like him," Regragui told a prematch news conference on Monday.