According to ESPN FC's Peter O'Rourke, the two clubs scouted him during Leipzig's match against Bayern Munich on Saturday, with Arsenal eyeing him as a long-term replacement for Petr Cech and Chelsea preparing in case Thibaut Courtois leaves.
Cech has contributed to plenty of clean sheets since he joined Arsenal, per WhoScored.com:
However, the stopper is now 35 and no longer inspires the level of confidence he once did, so it's good business for the Gunners to begin preparing for his departure. So too for Chelsea, who will not want to be left scrambling for a replacement for Courtois if another top club snap him up.