Iceland's 1-1 draw with Norway was enough to secure second spot in their group and they now go into the play-offs with the hope of securing their first- ever World Cup finals place.
Iceland, though, are unseeded and face a tough clash as they are likely to face Portugal, Greece, Sweden or Croatia.
But Sigurdsson believes Lagerback can take them further.
"He has been fantastic since he joined the team," Sigurdsson stated.
"He has brought experience from earlier qualifying campaigns and finals with Sweden and Nigeria."
And Lagerback hailed his Iceland squad after they made it to the play-offs.
"To qualify for the play-offs is of course a big achievement for all countries." he said.
"But this is truly something special. We were definitely the underdogs.
"When you are in the play-offs, everything can happen and with the team we have got, we can always win over two matches.
"Everything is possible, we can climb over volcanoes with these lads."