Lord Richard Dannatt, chief of general staff to the army from 2006 to 2009, said on Tuesday that the strange marks and colouration seen could suggest evidence he is receiving injections.
He told Sky News: "Another thing worth reflecting on is how healthy - or not - Vladimir Putin is.
"Keen observers now are noticing that his hands are looking pretty black on top, which is a sign of injections going in when other parts of the body can't take injections.
"It's interesting to note that, and just to watch whether he is as fit and well as he would like to portray. It's an interesting area to keep an eye on."
The health of Mr Putin has been a topic of conversation for months.
In May Russian Foreign Minister Sergei Lavrov was forced to deny President Putin is seriously ill after several reports he is being treated for blood cancer.
In July, CIA (Central Intelligence Agency) director William Burns said there was no evidence to suggest he was ill, adding, “As far as we can tell, he is absolutely too healthy”.
Mr Putin has stepped up the Russian effort in their conflict with Ukraine in recent weeks, pulling out of a UN-agreed deal to supply grain to countries in need.
Lord Dannatt said the fight around the Ukraine city of Kherson is “intensifying”.
He added: "It appears that the Russians have moved some of their better troops to defend Kherson.
"And if it was to be lost, it's a major defeat and a major embarrassment for Putin.
"As Kherson is the one major city that he has managed to capture so far, so on the battlefield the fight continues and at home, the fight continues."