Summer signing Van Nistelrooy has started all five of Malaga's Primera Division matches this season but has yet to find the back of the net, with his fellow new arrivals Santi Cazorla and Joaquin Sanchez netting six of the club's seven goals so far.
Nevertheless, Mathijsen, who played alongside Van Nistelrooy at Hamburg last season before also making the move to the south coast of Spain, believes the prolific 35-year-old will soon be back amongst the goals.
"Ruud is a striker and he likes to score. He had a good chance in Zaragoza and he'll shortly be back to scoring," said Mathijsen, who believes the rest of the team need to do their bit to help the strikers.
"We have to improve in attack, and that starts at the back, with the defenders, when the strikers don't get the right balls they don't score and that's what we need to improve."
Even without Van Nistelrooy managing to get off the mark, new-look Malaga have had an impressive start to the campaign, bouncing back from their opening-day 2-1 defeat to Sevilla to pick up 10 points from a possible 12 in their next four matches.
That has left Manuel Pellegrini's men in sixth spot heading into Saturday's visit of Getafe, just two points off leaders Real Betis.
Holland international Mathijsen, who has helped his side keep four successive clean sheets, said: "We're going through a good patch, and we're confident. It was a shame not to win against Zaragoza, we've got to improve but we've got a good feeling at the moment."
Getafe have not had such a good start but, after taking only one point from their opening four games, they claimed their first win on Monday night, and it was a noticeable scalp as they ended Betis' 100% record.
That victory lifted Luis Garcia's men out of the relegation zone, but they are still in the bottom five going into the trip to La Rosaleda.
Coach Garcia admits it will be tough against big-spending Malaga but pointed out his side gave Real Madrid a run for their money at the Bernabeu before losing 4-2 earlier this month.
"You talk of Van Nistelrooy, Joaquin, Cazorla..and it's clear that they will be at the top. It's one of the most difficult games of the season, but at the Bernabeu we showed that we can win these matches," he said.