So this seems to be a wrong track.
I found the following passage in "Lechicki początek Polski, szkic historyczny, skreślił Karol Szajnocha, we Lowowie, nakładem Karola Wilda, 1858", original PDF image + the OCR-digitized version by Google,
archive.org/details/lechichipoczate00szajgoog
As to adjectival Polish suffix -ski, it agrees with the Norman's -ske, once probably also -ski, and therefore it is one of the prehistoric monuments of commonality of both languages. Honorable meaning of noble surnames ending with -ski, has probably its roots in customs of ancient Normans - having the habit of giving honorable nicknames to illustrious people, originating from places of origin or countries heroically visited or conquered.
The ancient sagas refer to series of quasi-Polish names, ending in already forgotten suffix -ski (instead of -ske), going back to prehistoric terms of Nordic mythology: such as Oski (Grimm Myth. 390), Grenski, Swenski (Snorro 183), Liwski (Munch Her. Zeit 77), Tronski (Saxo Gr 92), Kolski (Grim Myth. 941), Haukdalski (Rafn Ant. 8), Hwinwerski (Snorro 14), etc.
Background:pl.wikipedia.org/wiki/Karol_Szajnocha
was a self taught historian, historiographer, writer and a proponent of various theories regarding the prehistoric beginnings of Poland. In 1858, refreshing the old theory of Count Thaddeus Czacki, he published the work "Lekhian (Lechian) beginnings of Poland". Szajnocha believed that the first Polish state was organized - in line with the so-called. invasion theory - by the the Scandinavian tribe of Lechians, forerunners of the later Polish nobility.
In many countries Lach, Lachs is also a common name referring to the Polish nation as a whole, or its parts, while Lechistan refers to the state of Poland. For example:
East-Slavic languages: Lach
Wallachian: Ljach
Bysantine: Lechoi
Hungarian: people Lendiel (Lengyel), country: Lengyelország
Persian: Lachistan or Lahestân,
Lithuanian: country: Lenkija, Lenkas - people
Turkish: Lehistan
High Icelandic: Læsialand
Armenian: Lehastan
Crimean Tatars: Lehistan/Лехистан
Kurdish: Lêhistan/Леһьстан or Lohêstan/Лоһестан,
We also know that Scandinavians used to refer in XI c. to Poles around Gniezno as "Laesar" (Lechici). According to Karol Szajnocha and Scandinavian historians the names Lach and Wareg mean the same: companion, ally.
The ancient sagas refer to series of quasi-Polish names, ending in already forgotten suffix -ski
Apparently Karol Szajnocha was right stating that the suffix -ski existed in Old Norse language. That suffix still exists in one of the closest cousin of Old Norse - the Faroese (Føroyskt) (another one is the nearly extinct Icelandic).
Here is an excerpt from the ballad "Long Serpent", in Faroese language. Below it there is a similar fragment, taken from English Wikipedia. It is evident that the Faroese uses the masculine forms of Polish-like adjectives in "svenski", "danski" and "norski".
Kvæðið um Ormin langa er yrkt eftir frásøgnini í Heimskringlu um tann tiltikna sjóbardagan við oynna Svøldur ár 1000, tá ið tann danski kongurin Sveinur Tjúguskegg, tann svenski kongurin Ólavur Skeytkongur og tann norski jallurin Eirikur Hákunarson herjaðu á Ólav Trygvason
fo.wikipedia.org/wiki/Ormurin_langi_(kv%C3%A6%C3%B0i)
The ballad Ormurin Langi (Long Serpent) takes its subject matter from the account well given in "Heimskringla" ('The Chronicle of the Kings of Norway') of the famous sea battle off the island of Svolder in 1000, when the Danish king Sveinur Tjúguskegg, the Swedish king Ólavur Skeytkongur, together with the Norwegian earl Eiríkr Hákonarson, attacked the Norwegian king, Olaf Tryggvason, while he was on his way home from Wendland to Norway on his ship, the Long Serpent, accompanied by his fleet.
[They attack in turn and King Olaf repulses the assaults of the two kings, but is defeated by his countryman Eiríkr Hákonarson.]
The outcome of the battle is known; when Olaf realises that the battle is lost, he leaps overboard together with his surviving men.en.wikipedia.org/wiki/Ormurin_Langi